Skip to main content

Full text of "Annual Reports of the Department of the Interior for the Fiscal Year Ended June 30, 1900--Twenty-First Annual Report of the United States Geological Society"

See other formats


jL~ / 






M 






ANNUAL REPORTS 

DEPARTMENT OF THE INTERIOR 



FISCAL YEAR ENDED JUNE 30, 1900. 



TWENTY-FIRST ANNUAL REPORT 

OF THE 

UNITED STATES GEOLOGICAL SURVEY, 

CHARLES B. WALCOTT, Director. 

1 J ART II. 



WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 
1900. 



TWENTY-FIRST ANNUAL REPORT 



UNITED STATES GEOLOGICAL SURVEY 



PART II.-GENERAL GEOLOGY. ECONOMIC GEOLOGY, ALASKA 



CONTENTS. 



Page. 
Cross, W., and Spencer, A. C. Geology of the Rico Mountains, Colorado 

(Pis. I-XXII) 7 

Mattiies, F. E. Glacial sculpture of the Bighorn Mountains, Wyoming (PI. 

XXIII) 167 

Turner, H. W., Knowlton, F. H., and Lucas, F. A. The Esmeralda forma- 
tion, a fresh-water lake deposit, by Mr. Turner; accompanied by a reporton 
the fossil plants of the formation, by Mr. Knowlton, and by a report on a 
fossil fish, by Mr. Lucas ( Pis. XXIV-XXXI ) 191 

Weed, W. H. Mineral vein formation at Boulder Hot Springs, Montana (Pis. 

XXXII-XXXIV) 227 

Taff, J. A., and Adams, G. I. Geology of the eastern Choctaw coal field, 

Indian Territory (Pis. XXXV-XXXVII) 257 

Taff, J. A. Preliminary report on the Camden coal field of southwestern 

Arkansas (Pis. XXX VIII-XXXIX) .• 313 

Brooks, A. H. A reconnaissance from Pyramid Harbor to Eagle City, Alaska, 
including a description of the copper deposits of the upper White and 
Tanana rivers (Pis. XL-L) 331 

Rohn, 0. A reconnaissance of the Chitina River and the Skolai Mountains, 
Alaska (Pis. LI-LIX) 393 

Schrader, F. C. Preliminary report on a reconnaissance along the Chandlar 
ami Koyukuk rivers, Alaska, in 1899 (Pis. LX-LXVIII) 441 

Baker, M. Alaskan geographic names 487 

Index 511 

5 



GEOLOGY OF THE RICO MOUNTAINS, COLORADO 



WHITMAN CROSS and ARTHUR COE SPENCER 



CONTENTS 



Page, 

Preface, 1 >y Whitman ( Iross 15 

Chapter I. Outline of the geology, by Whitman Cross 17 

Literature concerning the region 17 

Hayden Geological Survey _ 17 

John B. Farish 18 

T. A. Eickard 18 

Telluride and La Plata folios 19 

General description of the mountains 19 

Physiographic relations of the mountain group 19 

Drainage system and vegetation 20 

Details of physiography 20 

Structure of the Eico Mountains _ 21 

Elements of the structure 21 

Eico dome 22 

Relation to the San Juan structure 23 

Eelation of faults to the dome structure 23 

Relation of intrusive rocks to the dome structure 24 

Stratigraphy 25 

Sedimentary section represented 25 

Algonkian rocks 26 

Devonian 26 

Carboniferous - 27 

Permo-Carboniferous 27 

Juratrias 28 

Igneous intrusions 29 

Intrusive sheets 29 

Cross-cutting stocks 30 

Later dike rocks 31 

Contact metamorphism 32 

Volcanic phenomena 32 

Solfataric action 32 

Existing sulphur springs 33 

Carbonic acid exhalations 33 

Ore deposition 33 

Erosion of the Rico dome 34 

Recent geologic history 35 

Chapter II. The sedimentary formations, by Arthur Coe Spencer 37 

Algonkian 37 

' Introductory statement 37 

Relations of the Rico Algonkian 38 

Description of the quartzites 39 

Description of the schists 39 

Occurrences 40 



10 CONTENTS. 

Chapter II. The sedimentary formations — Continued. P age- 

Devonian 41 

General relations 41 

The quartzite _ 43 

The limestone 4.5 

Economic importance of the limestone 47 

Carhoniferous 47 

Hermosa formation 48 

Characteristics in the San Juan region 48 

Definition 48 

General description 48 

Animas section 48 

Description ami division of the Rico section 49 

< reneral statement 49 

Lower division 50 

Exposures of 1 1 • • - lower beds 50 

Medial division 53 

Upper division 57 

Fossils and correlation 59 

Rico formation 50 

Definition 59 

Discovery of the formation GO 

I '. scription 60 

Local distribution 62 

Correlation 64 

Juratrias 66 

Introductory lid 

Dolores formation i>7 

Definition 67 

General description and subdivision i>7 

i. unfossiliierous division 68 

Upper, foasiliferoufi division 71 

Distribution and occurrence 72 

I. a Plata formation 73 

Definition 73 

I •■ scription 74 

I distribution and occurrence 75 

( brrelation 76 

McElmo formation 76 

Definition 76 

ription and occurrence 76 

Correlation 77 

Cretaceous 77 

(ii upter J H. The igneous n.cks and their occurrence, by Whitman Cross. .. 79 

Petrography 79 

Monzonite 79 

1 ri m ral description 79 

Variations of the monzonite 81 

Relations to other occurrences 81 

Porpnyries associated with the monzonite 83 

Hornblendic monzonite-porphyry 83 

ral description 83 

I <■ composition products 85 

Relationships of this porphyry 85 

Porphyry of Calico Peak and vicinity 87 

Basic dike rocl - 87 



CONTENTS. 11 

Chapter III. The igneous rocks and their occurrence — Continued. page. 

Phenomenaof intrusion 88 

Porphyry masses 88 

Centers of eruption 88 

Stratigraphic distribution of sheets 90 

Small dikes 90 

Monzonite stock 91 

Form and dimensions 91 

Relation to porphyry sheets 91 

Phenomena connected with igneous intrusion 91 

Contact metamorphism 91 

Solfataric action 92 

Comparison of the Rico Mountains with laccolithic centers of eruption. . . 94 

The laccolithic mountain groups 94 

Stocks and laccoliths of the Telluride quadrangle 96 

Relations of the Rico Mountains 96 

Chapter IV. Structure of the Rico dome, by Whitman Cross and Arthur Coe 

Spencer 98 

Introduction 98 

The broad San Juan structure 99 

San Juan dome 99 

Rico and La Plata domes 100 

Relation of local domes to larger structure 100 

Structure of the Rico dome 101 

Elements of the structure 101 

Profile sections 102 

Amount of deformation by folding 103 

Uplift due to intrusive porphyries 104 

Deformation by faulting 105 

Bedding faults 107 

Quotation from Farish 108 

Description of the ' ' contact ' ' by Rickard 108 

Comment upon the quotations 109 

Origin of the bedding faults 110 

Origin of the dome 112 

Description of the faults 114 

Spruce Gulch fault 114 

Deadwood fault 114 

Faults of Dolores Mountain and vicinity 115 

Blackhawk fault 116 

Nellie Bly fault 118 

Last Chance fault 119 

Smelter fault 120 

Cross faults between Smelter and Last Chance faults 122 

South Park fault 122 

Area between the Smelter fault and Silver Creek 123 

Silver Creek fault 124 

Faults bounding the quartzite mass south of Silver Creek . . . 125 

Telescope Mountain fault 126 

Faults of C. H. C.Hill 128 

Other faults 128 

Chapter V. Landslides, by "Whitman Cross 129 

General statement 129 

Enumeration of landslide areas 130 



12 CONTENTS. 

Chapter V. Landslides— Continued. Page. 

North side of Horse Gulch 130 

South side of Horse Gulch and Darling Ridge 132 

Crest of Darling Ridge. 132 

Physiography of the slope 133 

Landslide block at the Puzzle mine L34 

"The Blowout " 135 

Western limit of the landslides 136 

Telescope Mountain and C. H. C. Hill 136 

Telescope Mountain 136 

C. II. C. Hill 137 

Damming of Dolores River 138 

Recent slipping in C. II. ('. Hill 139 

Magnitude of the landslide action 140 

Ridge between Burnetl and Sulphur creeks 141 

Land-lip Mountain 143 

Dolores Mountain and Newman Hill 14:! 

Region south of Blackhawk Peak 144 

Discussion of landslide phenomena 145 

Distribution of the landslide- L45 

Character of the landslides 146 

Relations to topography 146 

Relations to other Pleistocene phenomena 147 

A.ge of the landslides 147 

Relation to faults 148 

Origin of the landslide- 149 

t'n wren VI. Erosion of the Rico dome and recent geologic history, by Arthur 

Coe Spencer L52 

Erosion of the dome L52 

( ieneral statement 152 

Pre-Glacial erosion 154 

iation of the Rico Mountains 156 

Forms Of evidence 156 

Topographic c\ idence. L56 

Glacial debris 157 

Recent geologic history L60 

Post-* rlacial erosion 160 

Varieties of surface deposits 160 

Landslides 161 

Talus 161 

Surface wash 161 

Valley deposits 162 

Alluvial fans 162 

< 'alcareous spring deposits ' 163 

Ferruginous deposits 164 

i ias springs - 165 



ILLUSTRATIONS 



Page. 
Plate I. View from Blaekhawk Peak, looking northeast toward the San Juan 

Mountain.* 18 

II. View looking east from the divide at the head of McJunkin Creek.. 20 

III. View looking east across the Dolores Valley from the ridge north- 

east of Burnett Gulch 22 

IV. Blackhawk Peak and adjacent summits, from Telescope Mountain.. 24 
V. Dolores Mountain and Newman Hill, from the west side of the river 

near Iron Creek 26 

VI. Sandstone Mountain, from the foot of C. H.C.Hill 28 

VII. Calico Peak from the south 32 

VIII. Profile sections through the Pico dome 102 

IX. Looking up Horse Gulch from Sandstone Mountain 128 

X. Darling Ridge, from Sandstone Mountain 130 

XI. Landslide area on the north side of Horse Gulch, as seen from a 

point west of the "Blowout" 132 

XII. Details of landslide topography in the area on the north side of 

Horse Gulch 134 

XIII. A landslide trench on the south slope of Horse Gulch 136 

XIV. Landslide bench at the Puzzle mine, in Horse Gulch 138 

XV. Telescope Mountain and C. H. C. Hill, from Sandstone Mountain ... 140 

XVI. C. H.C. Hill, from near the mouth of Marguerite Gulch 142 

XVII. Landslide sink on C. H.C. Hill 144 

XVIII. Tree split by recent landslide movement, upper limit of C. H. C. Hill . 146 
XIX. View looking down the landslide ridge southeast from Expectation 

Mountain 148 

XX. South face of Landslip Mountain 150 

XXI. Alluvial fan at the mouth of Aztec Gulch 162 

XXII. Geologic map of the Rico Mountains, Colorado Pocket. 

13 



GEOLOGY OF THE RICO MOUNTAINS. COLORADO. 



By Whitman Cross and Arthur Coe Spencer. 



PREFACE. 

By Whitman Cross. 

The Rico Mountains, the area discussed in the accompanying report, 
are situated in southwestern Colorado near the headwaters of the 
Dolores River. The summits of this compact and rather isolated 
group lie within an oval area about 7 miles in diameter from east to 
west and 5 miles from north to south. Some 8 miles to the northeast 
is the southwestern front of the San Juan Mountains, and about 16 
miles to the south rise the northern slopes of the La Plata Mountains. 
The peaks are nearly all included within the northeastern section of 
the Rico quadrangle, but a few lie to the east of the one hundred and 
eighth meridian, in the Engineer Mountain quadrangle. 

The name "Rico Mountains" was first applied to this group of peaks 
in the course of the work leading to the present report. On the Hay- 
den map of Colorado the term "Bear River Mountains" was used for 
the same group, but that name has never come into local use, and 
would now be a misnomer, for it is connected with a nomenclature for 
important .streams which has also failed of acceptance in the settle- 
ment of the country since the issue of the Hayden map. On that map 
the stream now known as the "West Dolores " River was called "North 
Fork of Rio Dolores;" the main stream, now named the "Dolores River," 
was designated the " South Fork of Rio Dolores, or Bear River," and 
from the latter alternative name originated the term applied to the 
mountains in question. The tributary of the Dolores heading in the 
La Plata Mountains has long been known as Bear Creek. On the 
Hayden map it has the name " La Plata Fork." 

While the Hayden name for this mountain group has been rejected 
in local usage the engineers and miners of the region have failed to 
supply a new one, but the individual character of the group, both 
geologically and physiographic-ally, makes some name desirable, and 
that here adopted .seems most appropriate. The mining town of Rico 
is situated in the Dolores Valley, in the heart of the group. 

15 



16 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

A detailed survey of the Rico Mountains has been made both on 
account of the economic importance of the district and as a necessity 
in connection with the areal geological mapping of the San Juan and 
adjacent mountains, now in progress. In the course of this work the 
Rico quadrangle was taken up in 1897 and finished, with the excep- 
tion of the small area about Rico, where the geology was found to be 
so complicated as to require an accurate and detailed topographical 
base. It was also seen that an intelligent exploitation of the mineral 
resources of the district was practically impossible until such a geo- 
logical map should be available. 

In the summer of 1898 the topographical map was made, and on its 
completion the geological work was at once begun, but could not be 
finished before the snowfall of early winter. In the season of 1899 
the work was completed. During the work of the three years men- 
tioned Mr. Arthur ( '. Spencer was associated with the writer as assist- 
ant geologist. Messrs. Ernest Howe, R. I). George, and Jason Paige 
served at different time-, as volunteer aids. 

In L897 .Mr. ( '. AY. Purington, assistant geologist, examined the ore 
deposits of the district, but the determination to make a special map 
and report rendered it desirable to bave a correspondingly detailed 
study of the economic resources in the following year, and to tins 
duty Mr. George W. 'Tower, jr., was assigned, as Mr. Purington had 
meanwhile resigned from the Survey. Before preparing his report 
upon the Rico district Mr. Tower also left the Survey to engage in 
private business. As some of the most complicated portions of the 
region, including the Silver Creek Valley, were QOt thoroughly under- 
stood during Mr. Tower's work, a further study of the ore deposits 
in the lighl of the geology will be carried on by F. L. Ransome in the 
season t <\' L900. 



CHAPTER I. 

OUTLINE OF THE GEOLOGY 



Bv Whitman Cross. 



LITERATURE CONCERNING THE REGION. 

Hayden Geological Survey. — The country adjacent to Rico was 
visited by geologists of the Hayden Survey in 1874 and 1876. In the 
former 3 r ear the late F. M. Endlich examined the district to the east, 
the one hundred and eighth meridian, passing through Telescope Moun- 
tain, being apparently the general western boundary of his field of 
work. In 1876 W. H. Holmes made a rapid reconnaissance over an 
enormous area of the plateau country to the west. The complicated 
geology of the Rico uplift, coming on the border zone between the 
fields of different men working in different seasons, did not receive 
adequate attention, and the Hayden map of this area is, therefore, quite 
unsatisfactory. 

From his report for the year 1871 it would appear that Endlich 
visited Blackhawk Peak ("Station 37"), approaching it from the east, 
but that he did not examine any other part of the mountain group. 
Since no benefit can come to the present report from a critical review 
of Endlich's inaccurate observations and misconceptions regarding the 
local geolog} r , they will be passed over with brief comment. He pub- 
lished two profile sections running through Blackhawk Peak, but the 
data of these profiles, of the published map in the Geological Atlas of 
Colorado, and his statements of observations do not agree, and they 
are all decidedly erroneous in most particulars. What Endlich saw of 
the Rico dome structure was interpreted as a rather sharp anticline 
running along Silver Creek. Some of the intrusive sheets about 
Blackhawk Peak were observed, but it is difficult to understand on 
what basis the porphyry sheet of Hermosa Peak was extended west- 
ward along the divide to the summit of Telescope Mountain. Endlich 
later became the superintendent of the first smelter at Rico, but he 
published nothing further concerning the geology of the region. 

The Hayden map of the western part of the Rico Mountains is the 
work of W. H. Holmes, and the inconsistencies in stratigraphy about 
the head of the Dolores River are due to the necessaiy adjustment 
between his work and that of Endlich. Holmes established a section 

21 GEOL, FT 2 2 17 



18 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

of the Mesozoic formations to the west, which was expressive, adequate 
to the needs of the reconnaissance map. and in its general features is 
to-day recognized as correct. Endlich, on the other hand, had estab- 
lished an inadequate and partially incorrect stratigraphic section for 
the same formations, and where these two systems of mapping came 
together there was naturally a forced representation of unconformities 
by overlap which did not exist. This explains the drawing of the 
Harden map about the Rico Mountains. The porphyry masses of 
Elliott Mountain and Calico Peak were observed by Holmes from a 
distance ami represented with some approximation to correctness. 

Joint 11. Farish. -In L892 John B. Farish read a paper before the 
Colorado Scientific Society entitled On the Ore Deposits of Newman 
Hill, near Rico. Colorado. 1 The description of the ore deposits was 
preceded i,\ some general remarks on the geology. The structure of 
the mountains was recognized by Farish as a domal uplift, and con- 
cerning it lie says: '"The elevation of the mountains was associated in 
its origin with the intrusion of a laccolitic mass of porphyritic diorite, 
which may lie seen a short distance above the town. The amount of 
upheaval at the center of the uplift was several thousand feet. Its 
longer axis i> at right angles to the course of the river,and is so coin- 
cident with the corresponding axis of the laccolite." It is not evident 
what outcrops were assumed to represent the large laccolith, hut the 
sheet at the northern base of Newman Hill is referred to as an offshoot 
from it. The rock of the laccolith is said to he probably a " horn - 
blende-augite-porphyrite (a porphyritic diorite)." on the authority of 
R. C. Hills. Faults were recognized by Farish. hut probably only 
the minor ones of Newman Hill. 

The sedimentary rocks about Rico are stated \>y Farish to be 
" Lower Carboniferous and Carboniferous proper," but the grounds 
for the determination arc not given. 

T. .1. Richard. A detailed description of the Enterprise mine was 
published in L896 by T. A. Richard, then superintendent of the mine." 
In this paper there arc but few statements concerning the general 
geology. The strata about Rico are said to be fossiliferous and to 
belong to the Lower Carboniferous, and the common igneous rock 
is called porphyrite, with a concise description by R. C. Hills. 
Richard refer- to "a large dike of porphyrite" crossing the valley 
north of Rico, "making a fault which breaks the continuity of the 
country on cither >ide.*' It would appear that this reference, as well 
as that of Farish, above noted, concerning the supposed laccolith, 
must be to the mass of schists with small dikes of hornblendic por- 
phyry, but the position and importance of the fault are not further 
indicated. 

Soc, Vol. IV pp. 1M-164. 
-Trans. Am. Inst. Min. In-.. Vol. XXVI, pf. 906-980. 



cross] description of the mountains. 19 

The papers of both Farish and Rickard deal mainly with the Enter- 
prise mine and give many important details of the geology of Newman 
Hill, as thus revealed, to which reference will be made further on in 
describing this locality. 

Tell/wide and La Plata folios. — The first results of the resurvey of 
the San Juan region, now in progress, are contained in the Telluride 
folio, No. 57 of the Geologic Atlas of the United States, issued in 
1899. The southwestern corner of the Telluride quadrangle is situ- 
ated almost at the northern base of the Rico Mountains, 4 miles north 
of Telescope Mountain. While the structure of the Rico Mountains 
extends into the Telluride quadrangle but a very short distance, the 
Mesozoic formations there exposed are the same seen at Rico, and the 
discussion of several of them is fuller in the folio than in the present 
report. But the most important bearing of Telluride geology upon 
that of the Rico Mountains is in connection with the intrusive mon- 
zonite porphyries, the stocks of granular rocks, and the surface vol- 
canic series of the San Juan. The age of the Rico dome, the conditions 
at Rico at the period of its elevation, and other problems of local 
geology must be discussed in the light of the facts observed in the 
Telluride quadrangle. 

The La Plata Mountains, situated mainly in the quadrangle of the 
same name and lying directly south of Rico some 16 to 25 miles, 
are so analagous to the Rico Mountains in general character that their 
description in the folio now in press (Geologic Folio No. 60, La Plata) is 
in a measure supplementary to that of the Rico group. The domal 
structure is simpler because there are no profound faults, the intrusive 
porphyries are of the same general character as those of Rico, and there 
are several stocks of granular rocks, monzonite, diorite, and syenite, 
cutting the porphyry sheets. 

GENERAL DESCRIPTION OF THE MOUNTAINS. 

Physiographic relations of tin moy/ntain <jn>iij>. —The Rico Moun- 
tains form a small, compact group of peaks resulting from the deep dis- 
section of a local dome-like uplift of sedimentary and intrusive igneous 
rocks. This uplift appears on the eastern border of the Dolores 
Plateau, which is continuous westward with the Great Sage Plain of 
Utah, extending to the brink of the Colorado Canyon. The termina- 
tion of the Dolores Plateau on the line passing through the Rico and 
La Plata mountains is due to a change in the attitude of the underly- 
ing sedimentary formations. Beneath the plateau they are approxi- 
mately horizontal, but on the line mentioned they come un'der the 
influence of the monoclinal folding which has taken place in a broad 
zone adjacent to the San Juan Mountains. 



20 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. , 

The relations of the Rico Mountains to the Dolores Plateau are well 
illustrated by the topographic map of the Rico quadrangle. On that 
sheet the plateau surface is shown crossing the western boundary with 
a general elevation of about9,4:00 feet, rising very gradually for several 
miles and then merging into a gently dipping surface on the borders 
of the Rico uplift, a short distance beyond the limits of the special 
map. To the east of the Rico Mountains the country is of irregularly 
undulating- character, modified by a few prominent peaks of intrusive 
igneous rocks. PI. I exhibits the character of the /one between the 
Pico and San Juan Mountains as seen from near the summit of Black- 
hawk Peak, the bighesl of the Rico group. At a distance of 8 or 10 
miles rise the very rugged peaks of the San Juan. In the middle 
ground, on the right, is Hermosa Peak, caused by an intruded por- 
phyry mass which is probably continuous with the white cliffs of Flat 
Top. seen on the left hand of the view. The low mountain with a 
light-colored band on its southern face, about -l miles from Blackhawk 
Peak, presents a beautiful section of the white La Plata sandstone, 
dipping gently away from the point of \ iew under the influence of the 
Pico uplift. 

Another view of this licit of country east of the Kico Mountains is 
presented in PI. II. a photograph taken from the knoll (11,886 feet) 
on the divide northeast of Telescope Mountain, looking east toward 
Hermosa Mountain. In PI. XIX (p. L48) is shown the character of 
the country between the Rico and La Plata mountains. The crest line 
of the central portion of the \ iow i- Indian Trail Ridge, the divide 
connecting tin' two mountain group-, which is made up of red Triassic 
strata dipping at a low angle southwest and passing under the .Jurassic 
and Cretaceous beds on the right hand border of die \ iew. 

Drainag< system and vegetation.- The Rico Mountains are cut into 
two nearly equal parts h\ the Dolores River, which receives all the 
drainage from within the group and from its northern and southern 
-lope-. ( )n the western side a portion of the drainage is into the West 
Dolores River, and on the east beads one of the tributaries of the 
Animas River. 

Timber line in the Rico Mountains lie- between 11.500 and 12,000 
feet, and it- course may be traced in several of the illustrations 
accompanying the report. The tree- and shrubs are those common in 
the mountain- of Colorado, w ith perhaps greater variety than usual in 
the lower sheltered valley-. 

Details of physiography. A glance at the accompanying map (PI. 
XXII. in pocket) shows that the Rico Mountain- consist of a circle of 
high and rugged peaks, divided into two crescent-shaped halves by the 
Dolores Valley. There are twelve peaks, each exceeding 1.2,000 feet 

in elevation above sea Level, an I the narrow crest connecting them 
rarely -ink- below 11,500 feet on either side of the river. In passing 



cross.] STRUCTURE OF THE MOUNTAINS. 21 

through the group the Dolores receives several important tributaries 
on each side. These lateral gulches are all deep, with steep sides, and 
their streams are still actively engaged in the work of erosion. 

The forms of these peaks and gulches are illustrated in the pho- 
tographs reproduced on the accompanying plates. Pis. Ill and IV 
in particular show the details of form seen in the higher summits 
of the eastern side of the river. The photograph reproduced in PI. Ill 
was taken from the ridge leading southeast from Expectation Moun- 
tain and exhibits the western face of Dolores Mountain rising above 
the gentler slopes of Newman Hill. On the right is the gorge of Dead- 
wood Gulch, beyond which rises the porphyry summit of Whitecap 
Mountain. In the background appears Blackhawk Peak. 

PI. IV represents the same group of peaks as seen from Telescope 
Mountain, and here the true relations of Blackhawk Peak to the lesser 
summits are revealed. On the right hand is the double summit of 
Dolores Mountain, then Whitecap, and, rising above all, the mass 
of Blackhawk Peak and its north ridge. On the left is an analogue 
of Whitecap, due to a massive sheet of porphyry. In the distance on 
the right hand are the peaks of the La Plata group. In both of these 
views appear details of structure to be referred to further on. 

The character of several of the western summits of the group is 
illustrated in the other plates accompanying this report. The Dolores 
Valley above Burns is shown in PL XVI (p. 142), and the higher por- 
tion of the town of Rico is seen in PI. V in relation to Newman Hill. 

STRUCTURE OF THE RICO MOUNTAINS. 

Elements of the structure. — The Rico Mountains are due to forces 
which have been very local in their action. The principal structural 
feature is a dome-like uplift of sedimentary beds resulting from a dis- 
tinct vertical upthrust. A part of the elevation of the strata is clearly 
due to the intrusion of numerous bodies of molten material injected 
between the beds, after the manner of laccoliths. The intruded magmas 
were indeed very similar in composition to those which by their intrusion 
caused the uplift from which have been carved the Henry Mountains, 
whence the laccolith was first described, and it is altogether probable 
that the intrusions of the Rico Mountains were contemporaneous with 
those of the Hemy Mountains and of several other isolated mountain 
groups of the plateau country to the west, referred to as laccolithic 
groups. Several of these assemblages of peaks can be seen from the 
Rico Mountains, and the La Platas, commonly considered as of that 
character, are but a few miles distant. 

But the elevation of the Rico dome was not in large degree due to 
the intruded masses of molten material, and it appears certain that a 
part of the upthrust occurred after the magmas had solidified into rock. 



22 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

This conclusion is necessary because of the numerous and important 
faults occurring in the mountains, the dislocation upon which has 
plainly added materially to the uplift, and these faults traverse por- 
phyry sheets as well as sediments. In the present relations of the 
formations it is impossible to determine very accurately how much of 
the uplift was caused by the igneous intrusions. In was certainly equal 
to the mass o( the intruded magma, but as the heart of the dome has 
now been eaten away, the former extent of the porphyry bodies at the 
center of the dome can not he ascertained. A considerable disturbance 
must have been caused by the Large cross-cutting monzonite stock on 
the west side of the river, hut the exposures about this mass are so 
poor that the evidence of the part this intrusion has played is very 
unsatisfactory. 

The structure of the Rico dome is somewhat obscured, especially on 
its eastern side, by an earlier structure belonging to a broad zone 
about tlie San Juan Mountains. This consisted of a dip to the south- 
west, which has been reversed in the Rico uplift. 

Rico ,1,,,,,,. The general structure <>f this quaquaversal fold or up- 
lift can he clearly seen from any of the higher peaks of the group; 
especially in the mountains on the easl side of the Dolores there are 

man} g I exposures which render the structure visible at a distance. 

and while certain broad surfaces to the west of the river exhibit no 
structural details, the existing outcrops are in accord with the general 
conditions. The broad dome structure is expressed upon the geological 
map by the way in which the formation lines cross mountain slope and 
valley, and the symbols indicating strike and dip as determined at 
many points show both the prevailing si ructure and the local variations 
from it. By reference to several of the accompanying views an idea 
of the attitude of the strata may he gained. 

In PL III the outcrops of the ledges of massive limestone may be 
traced as they rise from Deadwood Gulch across the west face of Do- 
lores Mountain, owing to the southeasterly dip. while in PI. IV, the 
same strata are seen rapidly descending to the valley of Silver Creek, 
under the influence of the northeasterly dip there prevailing. At 
various other points of both views the structure is more or less evi- 
dent. The view of Sandstone Mountain. PL VI, exhibits the dip to 
the west of north present in the ridge Leading to Mount Elliott. 

The influence of the Rico uplift is distinctly limited in the Dolores 
Valley at a point about <i miles above town, and on the southwest less 
definitely at nearly tl miles distance, the north-south diameter of the 
visible dome being thus about 12 miles. The east-west diameter is 
approximately 15 miles, from a point about 3 miles east of Blackhawk 
Peak nearly to the West Dolores River. The vertical extent of the 
uplift is estimated at about 4,500 feet. 



cross.] STRUCTURE OF THE MOUNTAINS. 23 

Relation to the San Juan structure. — As .shown many years ago on 
the Hayden map of Colorado, the entire series of Paleozoic and Meso- 
zoic sedimentary formations exposed upon the flanks of the San Juan 
Mountains has been affected by a relative upward movement of the 
mountain area, and the strata are now seen dipping south, west, and 
north, away from the center of upheaval. It is clear that there have 
been several periods of movement, but the dominant one in producing 
the visible structure was that occurring at the close of the Cretace- 
ous period. The Rico Mountains are situated directly on the line 
where the influence of this San Juan pre-Tertiary continental folding 
dies out and the strata assume the nearly horizontal attitude which 
they maintain under the great stretches of plateau to the west. The 
strata east of the Rico uplift dip southwesterly at decided angles, while 
those to the west pass immediately under the Dolores Plateau. 

The attitude which the formations would now exhibit along the line 
of the Dolores Valley were it not for the Rico dome may be plainly 
seen from the areal maps of the Telluride and Rico quadrangles. In 
the southwest corner of the former, and only 6 miles northeast of Rico, 
the Dolores flows in a canyon whose rim rock is the Dakota sandstone 
lying in almost horizontal position — the floor of the Dolores Plateau 
over large areas. As the valley of the Dolores leaves the Telluride 
quadrangle the formations rise rapidly under the influence of the 
Rico uplift, but at the mouth of Bear Creek, 12 miles below Rico, the 
stream is again coursing in a typical canyon of the plateau country, 
the Dakota sandstone reappearing as the floor of the mesas or plateau 
remnants on either side. But for the Rico uplift the Dolores would 
be flowing in a canyon like those referred to, along the stretch where 
the Rico Mountains now appear. East of the valley there would be 
remnants of the Dakota, forming sloping mesas like those common in 
the Durango quadrangle. 

The relative ages of the broad San Juan structure alluded to and the 
local Rico uplift are inferred from the facts of the Telluride quadran- 
gle, where the Mesozoic formations are affected by the San Juan uplift 
and were greatly eroded before the beginning of the volcanic eruptions 
which characterized the early Tertiary. Yet intrusive porphyries like 
those of the Rico Mountains are later than the earlier volcanics, at 
least; so the presumption is that the Rico uplift was much later than, 
and entirely distinct from, the pre-Tertiaiy movements about the San 
Juan region. It may have been synchronous with some of the conti- 
nental movements of Tertiary time not yet clearly differentiated from 
older movements in this region. This conclusion is in harmony with 
all the evidence available as to the age of the intrusion of diorite and 
monzonite-porphyry sheets like those of the Rico Mountains in other 
parts of Colorado. 

Relation of faults to the <l<>nn structure. The map shows a large 



24 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

number of faults of sufficient magnitude to affect the geological map- 
ping, and there are many others upon which the dislocation is very 
slight or not determinable. 'While there does not appear to he any 
definite system in the arrangement of these faults, it is true that they 
are for the most part confined to the area of uplift, and that their 
combined effect has been to increase the uplift near the center of the 
dome. Several of the important faults are so imperfectly exposed. 
owing t<> landside d6bris and other surficial materials, that the availa- 
ble data concerning their relations toother faults and to the domal 
uplift are far from satisfactory. It is reasonably certain, however, 
that faulting has occurred at different periods, and that the later 
faults arc of relatively recent age. 

It seems natural to assume that fissures would develop contempora- 
neously with domal uplift of any considerable magnitude. If the 
quaquaversal folding continued after the porphyry intrusions, the 
presence of these local and comparatively rigid masses would cause 
fractures in the adjustment of materials. Hut it appears that the 
fractures and dislocations just referred to must have been in large 
degree in the upper portions of the dome, now entirely removed by 
erosion, while as a matter of fact the existence of important faults 
beneath the Paleozoic sediments and all known porphyry bodies, and 
bounding hloek- of Aigonkian quartzite and schist, demonstrates the 
essentially deep-seated character <>( much of the observed fault frac- 
turing. 

The greater number of fault- located in the outer portions of the 
uplift exhibit an upthrow on the inner side, if their strike is tangential 
or approximately so, and in such cases the faulting has added to the 
elevation of the central parts of the dome due to the quaquaversal 
fold. In other case-, however, the faults are reverse faults, or hound 
blocks which have sunk. In the valley of Silver Creek, where the 
Aigonkian quartzites appear, it is often evident (hat the adjustment 
of the wedge-shaped blocks ha- been accomplished by many fractures, 
the relative importance of which it is impossible to establish. From 
the fault phenomena of this central region it appears that the faults 
represent a very strong vertical upthrust, and while some of them 
may have originated during the domal uplift, some of them, espe- 
cially the more recent one-, resulted from a force acting more ener- 
getically and causing rupture rather than bending of the rocks. 

The more detailed discussion of the faults in Chapter IV, with pro- 
tile sections, gives the basis for the above general statements. 

Relation of intrusivi rocks to t/u dome structure. — The masses of 
porphyry, bearing more or less distinct resemblance to laccoliths in 
their form and relation to stratification planes, have manifestly caused 
an uplift of the beds above them, and a- there is a distinct association of 
these masse- with the center of uplift, their combined effect would 



STRATIGRAPHY. 25 

alone have produced u domal structure of some magnitude. An 
examination of the map shows that the larger number of porphyry 
masses occur at horizons above the Carboniferous in the main circle of 
peaks and that only one or two sheets of importance occur in the 
Lower strata in the center of the dissected dome. The porphry sheet 
of Newman Hill and the Montelores sheet are the ones in question. 
If the form of the porphyry occurring- in Nigger Bab}' Hill were more 
plainly defined, it would possibly constitute a third body of note. But 
it seems hardly open to question that the main uplift of the Rico dome 
is disconnected from the intrusion of the visible sheets of porphyry, 
nor is there an} T evidence of concealed masses of that rock of any con- 
siderable magnitude. Until the presence of the Algonkian rocks was 
determined the writer entertained the working hj-pothesis that a large 
laccolith of porphyry might have been intruded at a horizon near the 
base of the Paleozoic formations, but the appearance of the pre- 
Paleozoic rocks in the heart of the mountains, with no evidence of the 
hypothecated laccolith, renders it improbable that the uplift can be 
primarily connected with porphyry intrusion. It is, then, much more 
likely that the intrusions are accompaniments or consequences of the 
local folding than that they are its cause. 

The monzonite stock of Darling Ridge is large enough to have pro- 
duced much disturbance of the sedimentary rocks above it— on the 
assumption that it did not reach to the surface — but erosion has 
entirely removed the rocks which could exhibit that disturbance. 
The lateral effect of this intrusion is almost entirely masked by land- 
slide debris, but what little evidence there is upon this matter indi- 
cates an astonishingly small amount of disturbance in the rocks 
penetrated. This particular stock does not, however, differ in this 
respect from the larger ones of the Telluride and Silverton quad- 
rangles or from the more nearly analogous masses occurring in the La 
Plata Mountains. The stock intrusion is later than the porplryry 
injections, and may be later than the greater part of the central uplift. 

STRATIGRAPHY. 

Sedimentary sect i<>n n i>r<s,nt< <1. — In the discussion of structure it 
has been stated that Algonkian schists and quartzites are exposed in 
the heart of the Rico Mountains. These rocks correspond to the pre- 
Paleozoic formations which, in association with older gneisses and later 
intrusive granites, clearly underlie the Paleozoic series on the south 
side of the San Juan Mountains, revealed with especial clearness in 
the Animas Valley and its tributaries. The successive sedimentary 
formations found in the central part of the Rico dome correspond to 
the Paleozoic portion of the Animas section, embracing Devonian, 
Carboniferous, and Permo-Carboniferous formations. All of these old 



26 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

geological formations have been brought to light at this point by the 
Rico uplift and its subsequent dissection by the Dolores River. As 
has been stated in an earlier paragraph, the bed of the Dolores at Rico 
would have been in the uppermost layers of the Triassic red beds were 
it not for the local uplift. 

The area of the special map exhibits the full thickness of the Trias 
and of the lower member of the Jura, but the Cretaceous sandstone 
and shale normally represented in the plateau adjacent to the Dolores 
Canyon have been entirely eroded away from the area covered by the 
map. though present on the northwest and south at no great distance. 
Chapter II contains a detailed description of the sedimentary forma- 
tions, hence the following statement- are such as seem necessary to 
this outline. 

Algonkian rocks. — The pre-Paleozoic quartzites and schists which 
appear as fault blocks thrust up into the Devonian and Carboniferous 
Strata at the center of uplift are of interest as indicating the extension 
of these oldest sedimentarie- westward under the Dolores Plateau. 
The locality is too near the great exposures of the Needle Mountains 
and of the Incompahgre Canyon to add much to the force of the sug- 
gestion that the latter locks may lie the direct eastward extension of 
the greal Algonkian series of the Grand Canyon of the Colorado, 
described by Walcott; but the evidence of the Rico outcrops, so far 
as it goes, is in favor of such a hypothesis. 

The blocks of quartzites on tl pposite sides of Silver Creek are 

very massive and highly indurated rocks, in which the original bedding 
is visible only on close examination. They resemble strata that are 
exposed in the Incompahgre Canyon near the mouth of Red Creek, 
in the Silverton quadrangle. The schists crossing the Dolores above 
Rico are likewise similar to rocks known in the Needle Mountains, 
but a- this latter complex has not yet been examined in detail, no sug- 
gestions of dose correlation for the Rico exposures can he made at 
this time. 

Devonian. — The lowest Paleozoic formation- exposed in the heart of 
the Rico uplift have been referred to the Devonian. There are two 
formations thus correlated, a limestone and an underlying quartzite. 
The former is the highly metamorphosed rock exposed in the main 
street of Pico and on the banks of the Dolores. The quartzite is shown 
in but a few small outcrops, and the base is not revealed. 

The reference of these strata to the Devonian is based more upon 
comparison with the Animas section of the Paleozoic than upon any 
direct evidence obtained at Pico. The thickness of the Carboniferous 
formation at Rico is sufficient, in the absenceof contrary evidence, to 
warrant the opinion that the limestone in question belong- to the 
Devonian, and the thickness of the limestone and the character of the 
fossiliferous Carboniferous strata just above it and of the quartzite 













w 


'' r #* '.J ' 






f 


;<". ^tL • ' ! Si -» 






rm.W; r. '.A ..'"*' , -, . 



cross.] DEVONIAN AND CARBONIFEROUS STRATA. 27 

below, indicate that the correlation is correct. The limestone exposed 
at several points on the Atlantic Cable claim exhibits an unusual 
structure, due undoubtedly to metamorphism. It consists of white 
granular marble in pure masses, an inch to a foot or more across, 
separated by a dark-green network of dense texture, composed chiefly 
of iron- bearing silicates. The exposures of this rock do not satis- 
factorily indicate its thickness, but a bore hole was sunk in it by the 
Atlantic Cable Company, which was prompted to its exploration by the 
nests of galena, magnetite, and other ores outcropping locally on the 
surface. The bore hole showed the limestone to have a thickness of 150 
feet, and to be underlain by quartzite, in which the drill was stopped 
after penetrating to a depth of 343 feet. As explained by Mr. Spencer 
(Chapter II), it must be inferred that the botton of the drill hole is very 
near the base of the quartzite, assuming the limestone to be Devonian. 

The metamorphosed limestone, if Devonian, is equivalent to what 
has been called the Ouray limestone, because of its typical develop- 
ment near the town of that name. 1 

Carboniferous. — A glance at the geological map shows that the 
greater part of the interior of the Rico Mountain group is composed 
of the Hermosa formation, of which three divisions may be made 
for purposes of description. The lower division consists chiefly of 
greenish-gra}' sandstones and shales, the latter being sometimes 
nearly black. The middle member is characterized by many bands 
of massive dark-gray limestone, often highly fossiliferous, alternating 
with sandstones and conglomerates. The upper division is predomi- 
nantly a complex of shales, with occasional limestones. 

The massive limestones of the middle member of the group form 
the most prominent outcrops of the entire formation. They are most 
marked on the west face of Dolores Mountain, on the banks of Silver 
Creek, and in Sandstone Mountain, as illustrated in Plates III- VI. 
The lower member is more friable in texture and forms less promi- 
nent exposures. The upper division corresponds more nearly to the 
succeeding formations in lithological character, and forms many ledges 
and cliffs at the horizons of its more massive conglomerates and 
sandstones. 

Most of the limestone layers throughout the formation are to some 
extent fossiliferous, and from the extensive collections which have 
been made it appears that the 1,800 feet of strata belong to one pale- 
ontological unit. The complex of strata characterized by this fauna is 
here named the Hermosa formation, from its typical development in 
the region of Hermosa Creek, a prominent western tributary of the 
Animas River, heading a few miles directly east of the Rico Mountains. 

Pernio- Carboniferous. — Succeeding the Hermosa formation comes 

i Arthur (J. Spencer, Am. Jour. Sci. 4th scries, Vol. IX, 1900, pp. 125-133, 



28 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

the great "Red beds" series of southwestern Colorado, in the upper 
portion of which Triassic fossils have been found at many localities. 1 
The change from the prevalent grayish tones of the Carboniferous 
strata to the distinct dull-red hues of the next higher beds is in 
general a rather sharply defined one, and the lower limit of the Trias- 
sic would undoubtedly have been drawn upon that criterion had the 
closer study of the section not revealed an important invertebrate 
fauna of Carboniferous affinities in several calcareous strata of the 
lower 200 or 300 feet of the reddish complex. This discovery, first 
made by Mr. Spencer, has led to the recognition of a persistent and 
well-defined formation which, on the authority of G. H. Girty, is 
referred to the Permo-Carboniferous, as expressing the fact that its 
fauna is intermediate in character between that of the true Permian of 
the Missouri Valley and the Carboniferous. 

Juratrias. — The sedimentary section between the Rico and the 
Dakota formations is subdivided in the Rico region, as in the Tellu- 
ride quadrangle, into three formations. The lowest of these is named 
the Dolores formation. It embraces hereabout 1.S00 feet of strata. 

for the most pari of the usual character of the Red beds, as known 

in Colorado. Fragmentary remains of dinosaurs and crocodiles of 
Triassic types occur in the upper part of the formation throughout 
the San Juan region and adjacent parts of the plateau country to the 
west. The fossiliferous portion of the formation is characterized by 
peculiar tine-grained limestone conglomerates and gray fissile sand- 
stones and shales, hut is by no means free from red sandstones and 
grits similar to those which prevail in the lower part. Detailed sec- 
tions showing the constitution of the Dolores format ion are given in 
the nexl chapter, together with a discussion of its relations to the 
Rico beds. 

Succeeding the Dolores formation comes the La Plata sandstone, of 
assumed Jurassic age. This formation consists essentially of two mas- 
sive, white, quartzose sandstones with a variable and subordinate, 
darker, calcareous series of shales, etc.. Let ween them. The thickness 
of the La Plata varies in the Rico region from 250 to 500 feet. Tt is 
present not only in the western part of the area of the special map, 
but is found on the borders of the dome on the north, east, and south 
as well. 

The third member of the Juratrias, and the uppermost of the Meso- 
zoic formations preserved in the area of the accompanying ma]), is the 
McElmo formation. This consists of alternating fine-grained sand- 
stones and variegated marls or clays in a total thickness of ■"><>() feet, of 
which only the lower portion is preserved in the area mapped. The 
McElmo strata are lithologically very similar to the Morrison beds of 

'Geologic Atlas I - i>lio57, Ti lluride, I olo. 



cross.] INTRUSIVE SHEETS. 29 

the foothills of the Front Range, so celebrated for their dinosaurian 
fauna of Jurassic types, and occupy a corresponding position with 
regard to the Dakota formation. 

IGNEOUS INTRUSIONS. 

The geological map represents a large number of masses of igneous 
rock, of varying size and form, distributed throughout the Rico 
Mountains from the center to the outskirts. Similar rocks occur, in 
fact, at scattered points over a large area about the mountains, but it 
is plain that the center of uplift was also a notable center of eruptive 
activity. Viewed from the standpoint of their geological occurrence, the 
igneous masses may be classified as intrusive sheets, stocks, and dikes. 
The former acted collectively to add to the domal uplift caused by 
folding and faulting. The stocks have cut directly across the strata at 
the horizons now exposed and do not visibly affect the general struc- 
ture. The dikes are the rilling of narrow fissures and were formed at 
several periods. 

Intrusive sheets. — Intrusive porphyry bodies, which may be called 
sheets, occur throughout the sedimentary section from the base of the 
Hermosa (Carboniferous) to the Cretaceous. Their distribution, both 
geographic and stratigraphic, and the forms of the outcrops are shown 
on the geological map. The original form and extent of many of these 
porphyry bodies are not now determinable, since they occur in the 
higher peaks, and the remnants left by erosion may represent either 
extensive or local masses. There are, however, numerous bodies pos- 
sessing a lateral extent many times their thickness intruded at or near 
a definite horizon, and these must be called sheets or sills. Of other 
masses, such as those forming the summits of Elliott and Whitecap 
mountains, there is little evidence of the original shape except that 
their bases are conformable to the strata below. No definite dome- 
shaped porphyry mass or laccolith has been observed in the Rico 
Mountains, and such thick sheets as those present in Blackhawk Peak 
and elsewhere are large enough to have produced isolated remnants 
like those of the summits above named. 

The statement by Farish in the article already cited, that a laccolith, 
supposed to have played the principal role in the Rico uplift, is visible 
just above the town, may have had reference to the monzonite stock of 
Darling Ridge or to the Algonkian schists shown on the map. The 
hypothesis that the elevation of the strata was clue to a buried laccolith 
was a natural one in view of the presence of so many porphyries nearly 
identical with those of the Henry Mountains in composition and struct- 
ure, but no evidence of such a mass has been found. 

While some sheets follow definite horizons for the entire extent of 
present exposures, others cut across from one stratification plane to 



30 GEOLOGY OF THE EICO MOUNTAINS, COLORADO. 

another or split into two or more branches. These evidences of the 
intrusive character of the porphyries arc abundant. By extended 
cross-cutting courses at angles oblique to the stratification transitions 
between sheets and dikes are formed, and these bodies are by no 
means rare. It seems probable that whole groups of porphyry masses, 
such as those in and about Blackhawk Peak and those in the summits 
around Anchor Mountain, were contemporaneous in origin and con- 
nected by many cross-cutting arms. In the latter region especially 
much evidence of this connection is visible and has been expressed on 
the map. 

The largest sheet now preserved, and the one occurring at the lowest 
horizon, is that at the northwest base of Newman Hill. It. has a thick- 
ness of at least 500 feet, and its lateral extent may be much greater 
than the portion seen. 

The rocks of the intrusive sheets are of a type common in the moun- 
tains of Colorado and in the isolated groups of the plateau country. 
They are all pronounced porphyries, with many small white plagioclase 
crystals, with smaller prisms of hornblende, and occasionally crystals 
of quartz, all embedded in a gray fine-grained groundmass, which con- 
sists chiefly of orthoclase and quartz. Some variation in the propor- 
tions of the constituents occurs without any marked change in habit, 
except that either a decided increase in the amount of hornblende or 
its development in very minute particles causes a darker color. All 
the sheet rocks and main dikes are included petrographically under a 
single name, moii/oiiite poiplix iv. expressing the composition, in 
which the alkali feldspar, orthoclase. and the soda-lime feldspar, pla- 
gioclase, are estimated to play approximately equal roles. The further 
composition of the rock is expressed by saying that it is a quartz- 
bearing bornblendic monzonite-porphyry. 

Gross-cutting stocks.- The large mass of quartz-monzonite on Dar- 
ling Ridge is a type of the eruptN <• body known as a stock. This body 
exhibits no tendency to spread out laterally on stratification planes. 
but cuts almost vertically across every rock in its path. It has no 
regular outline and its original upper limit is entirely a matter of 
inference. No doubt it penetrated to much higher levels than those 
now seen, but there is no instance known to the writer where the 
upper extremity of such a stock i- exposed, although in the San Juan 
Mountains similar rocks are found cutting the highest bedded volcanics 
now remaining. 

The stock contacts are mainly concealed by landslide or other debris: 
hence there is more or less assumption in the statement that the sheets 
of porphyry coming in contact with thestockare invariably cut by it. 
Yet the complete correspondence between the eruptive phenomena of 
the Rico and La Plata mountains makes it probable, in the absence of 
any contrary evidence, that the two forms of occurrence bear the same 



cross.] STOCK AND DIKE KOCKS. 31 

relations in the two localities. In every locality thus far known to 
the writer where these forms of occurrence arc associated the stocks 
cut the sheets. 

The rock of the Darling Ridge stock is a typical monzonite, similar 
to that of certain stocks in the La Platas and to that in the great stock 
of Grizzly Peak, in the southwest angle of the San Juan Mountains, 
or in Sultan Mountain, near Silverton. It appears like a diorite 
at first sight, and would have been so called a few years ago, but a 
pink alkali feldspar, orthoclase, is associated with an equal or larger 
amount of white soda-lime feldspar, throwing the rock into the new 
group proposed by Brogger, intermediate between syenite and diorite. 
There are many rocks of this character in Colorado and elsewhere in 
the Rocky Mountains, and the new division is a very welcome one to 
petrographers working in these districts. As will be shown in Chap- 
ter III, the presence of a small amount of quartz -brings the Rico 
monzonite into close relation with the quartz-diorites and the quartz- 
bearing syenites. 

Later dih rocks. — While the hornblendic monzonite-porphyry intru- 
sions and the monzonite stock are by far the most important of the 
igneous masses in the Rico Mountains, two other eruptions have been 
recognized which have considerable interest from the theoretical stand- 
point. These two eruptions produced rocks of very different charac- 
ter, the one containing numerous large orthoclase crystals and being a 
strongly marked porphyry, while the other type is a very dark, dense, 
aphanitic rock, few of the mineral particles being determinable by the 
unaided eye. 

The rock characterized by large orthoclase crystals occurs in several 
dikes in a band running east and west through Johnny Bull Mountain. 
Its most prominent dike, and also the longest shown on the map, 
crosses the divide between Calico Peak and Johnny Bull Mountain. 
The rock is in composition a monzonite-porphyry in which orthoclase 
assumes a prominent position in large phenocrysts, while plagio- 
clase occurs in part in the groundmass. The rock is more closely 
related to the stock monzonite in composition than to the earlier horn- 
blendic monzonite-porphyry. Its dikes cut many sheets of the latter 
rock, establishing the time relation of the two varieties, but, so far as 
observed, it does not come in contact with the stock monzonite, and it 
is therefore not definitely known which of these rocks is the older. 

The dark aphanitic rocks occur in narrow dikes scattered sparingly 
all through the mountains and probably for many miles about them. 
Similar dikes have been noted in the vicinity of most of the diorite 
and monzonite stocks of southwestern Colorado, and they are always 
later than any other intrusive rock of the regions where they have 
been found wherever relative ages could be determined. In the Rico 
Mountains but one dike was seen cutting the stock rock. The small 



32 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

size of the dikes make them quite inconspicuous and they can seldom 
be traced for considerable distances. 

In Chapter III will be given the reasons for naming the aphanitic 
dike rocks of the Rico Mountains olivine-bearing (mgite-vogesites. 
Perhaps they do not all belong to this type, but the questionable ones 
are much decomposed and their original constitution is a matter of 
conjecture. 

The theoretical interest of these vogesites is that they may lie 
regarded as products of magmatic differentiation from the monzonite 
magma, which is clearly the principal one of this eruptive center. 

CONTACT METAMORPHISM. 

Contact metamorphisni of tin- calcareous strata adjacent to the mon- 
zonite stock is very pronounced at nearly all places where the former 
rocks arc exposed in tli<' vicinity of the intrusive. The character of 
the metamorphisni is such as might be expected from the action of 
such mineralizing agents as chlorine, fluorine, and heated water car- 
rying those gases and perhaps others in solution. The metamor- 
phisni referred to consists in the formation of garnet, pyroxene, vesuv?- 
anite ('.). and possibly other silicates of alumina, with magnesia, iron, 
and lime, and in the deposition of specular iron in scales, either impreg- 
nating the rocks or. more coininonlv. in thin crusts in fissures. Such 
alteration of the calcareous strata may he seen on the north side of 
Darling Ridge, near the Blowout in Horse (iulcli. and down near 
Piedmont. If the metamorphosed stratum is a limestone the matrix 
for the silicates named is usually white crystalline marble. 

The great metamorphisni of the Devonian limestone in the Dolores 
Valley at Rico is so clearly of the character known as a contact phase 
of the kind described that it is considered probable that this change is 
also due to the monzonite intrusion. The eastern end of the monzonite 
is just above the street in Piedmont, and there must have been fissures 
traversing the strata in the prolongation of the principal axis of the 
stock. These may have given heated solutions the necessary access to 
the limestone at the places now seen. So far as observed, such con- 
tact metamorphisni is confined to the zone about the stock with the 
exception of one place in the shattered zone, between the forks of the 
Blackhawk fault, where garnet masses and specular iron occur near a 
small porphyry dike. 

VOLCANIC PHENOMENA. 

Solfataric <i<tn>i,. — While no evidence can ever he disco\ ered prov- 
ing that the surface phenomena ordinarily known as volcanic attended 
the deep-seated intrusions in the Rico dome, there have been certain 
processes active in the horizons now revealed hy erosion which are 
generally supposed to characterize zones near the surface. One of 









fl ap 1 


















j 












••TJ5^2 


» 






F 


' 




Jm 


is* 


. •' 




\ 








\> 


7 ■ \ 




m* ;• 


J 


9& ] 


PP* 


j 




Hi ^"^iiImM 


> 





CB06S.] VOLCANIC PHENOMENA. 33 

these processes is the decomposition of rocks by sulphurous vapors, or 

by solutions that have absorbed those vapors, and the production of the 
hydrous sulphate of alumina and potash called alunite. This substance 
is formed at the surface in the crater of Solfatara, near Naples, and 
is a common product of the sulphurous emanations of volcanoes known 
from this locality as solfataric exhalations. But the process is not 
necessarily connected with solfataras of typical volcanoes, and the term 
has been gradually extended to cover the metamorphosing action often 
consequent upon eruptions which have been accompanied by mineral- 
izing agents of sulphurous character, even when taking place in depth. 

The orthoclase-bearing porphyry mass of Calico Peak has been 
almost wholly decomposed by-such agents, alunite and kaolin being 
the principal products. The rock now appears as a white porphyritic 
mass of quartz and kaolin, but closer examination reveals much alunite. 
These rocks of Calico Peak are more fully described in Chapter III, 
with chemical analyses. 

Existing sulphur springs. — It is especially notewortlry in connection 
with the evidence above given of former intense solfataric action, that 
there are numerous springs of water heavily charged with sulphureted 
hydrogen issuing to-day from the slopes of Stoner and Bull creeks 
and of other tributaries of the West Dolores north of Bull Creek. As 
noted by Mr. Spencer in Chapter VI, the waters of these springs are 
surface waters, as they are influenced directly by rainfall and dry up 
at times, but the sulphurous gases escape continuous^. The presence 
of these springs on the west side of the dome only, in an area extending 
from the immediate vicinity of the solfataric center at Calico Peak 
toward the West Dolores, suggests that these exhalations really belong 
to a later solfataric period of this eruptive center. 

Carbonic add i-.rji nlatlons. — The water of several springs issuing 
from the gravels of the Dolores stream bed near the Shamrock tunnel, 
in the town of Rico, are very highly charged with carbonic acid gas. 
Other springs of similar character occur at several places in the valley 
above the town, and the calcareous spring waters also carry some 
excess of this gas. 

In several tunnels driven into the west bank of the Dolores near 
Rico, in a bore hole on the Atlantic Cable claim, in the Rico-Aspen 
property, and at many other points in the district, carbonic acid gas 
has been encountered, often under considerable pressure, reaching as 
much as 55 pounds to the square inch in the case of the Atlantic Cable 
drill hole. 

ORE DEPOSITION. 

After the uplift of the Rico dome, the intrusion of the igneous 
rocks, and at least a portion of the fault Assuring, there was a period 
of extensive ore deposition in the rocks now forming the Rico Moun- 
21 GEOL, I'T 2 3 



34 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

tains. While the age of the ore deposits can not be closely deter- 
mined, it is in every way probable that they correspond in time to the 
deposits of the La Plata Mountains and that they belong to the great 
epoch of ore deposition which succeeded the early Tertiary igneous 
intrusions or more typical volcanic eruptions in many parts of the 
Rocky Mountains. Apparently the more typical laccolithic mountain 
groups of the plateau country to the west do not contain ore deposits 
in an abundance at all corresponding to their development in the La 
Plata and Rico mountains, but whether that fact is connected with 
their situation, remote from the great centers of eruptive activity, or 
to local causes can not now be determined. It would, however, appear 
natural that more extensive deposition of ore minerals should occur in 
a center like the Rico Mountains, where there has been SO unusual an 
amount of Assuring, affording channels for the circulation of metal- 
bearing solutions. 

In view of the forthcoming special report upon the ore deposits of 
the Rico region, by Mr. Ransome, the treatment of these masses in 
this place must necessarily be restricted to their general geological 
features. The ore-, occur in veins, iii shattered zones of both sedi- 
mentary and igneous rocks, as replacements of lime-tone and of other 
rocks in less degree, and as variable impregnations of country rock. 
In mineralogical character the ores are principally sulphides of iron, 
had. copper, and zinc, which are variably argentiferous and rarely 
have a small value in gold. Rich silver minerals occur sprinkled 
through the ore- of Newman Hill and of some other localities. Many 
of the known large bodies of |>.\ rite are too low in precious metal 
values to be of present economic importance. Descriptions of the 
mines of Newman Hill by Farish and Rickard have been referred to 
in an earlier section of this chapter. 

EROSION OF THE RICO DOME. 

As explained in detail in Chapter IV. it i- evident that the dissec- 
tion of the Rico dome and the production of the existing topography 
must have taken place before the epoch of local glaciation and before 
the beginning of the landslide epoch. It therefore occurred in a time 
interval for which we have no chronological criteria to apply in this 
case. The evidence of the age of the igneous intrusions has been 
given, and all that can he said with certainty i- that the dissection 
must have occurred after the uplift, and that it was practically com 
plete before the landslides began and before the local glacial epoch. 

How the Dolores River came to cut il- way through the heart of the 
Rico dome rather than through the much softer sedimentary beds to 
the west is a problem of much interest. Hut upon this question there 
is little evidence now remaining, fni- the erosion of the whole country 



cross.] LATER GEOLOGIC CHANGES. 35 

adjacent to the San Juan has been so extensive that all conceptions 
of the surface conditions determining' the Tertiary drainage systems of 
the region are extremely hypothetical. 

RECENT GEOLOGIC HISTORY. 

Since the great erosion by which the Rico Mountains were produced 
the history of this district can bequite clearly read in the arrangement 
and character of the superficial materials now seen in the valleys and 
on the mountain slopes. Where sculpturing of the mountains has 
taken place in the higher portions of the district there is evidence — 
which will be apparent later on — that the streams have cut but little 
into the solid rock in all the lower parts of their courses. In the 
higher parts of the mountains, however, the ordinary atmospheric 
agencies have been active and large amounts of talus and slide rock 
are seen on many of the steeper slopes. 

The greatest change in the physiography of the region since the 
great erosion has been effected through the agency of landslides. 
Throughout the larger tracts which are shown on the map the land- 
slides have modified the form of the ridges and mountain slopes and 1 
have to some degree filled up the valley bottoms, especially of the 
Dolores opposite C. H. C. Hill and of Horse Creek. Apparently the 
streams in their lower courses have not as yet been able entirely to 
remove this landslide debris. 

Glaciation of the Rico Mountains has been confined to the upper 
levels and to the narrow stream beds. At least, the evidence of gla- 
ciation to be determined from debris and forms of erosion does not 
indicate that any very large part of the mountains was covered with 
glacjal ice. 

In the valley of the Dolores there are various deposits of stream 
gravels, and the map shows the distribution of the more recent deposits. 
Remnants of terraces in several places indicate former deposits, but 
these are not always clearly distinguishable from debris of other 
origin. 

While the lateral tributaries of the Dolores have no bottom deposits 
of importance, several of them have built up very decided alluvial 
cones at their mouths. The more important of these are represented 
on the map. 

Small deposits of calcareous sinter or tufa have been noted at various 
points on the banks of the Dolores, and several of them are shown on 
the map. At a number of these points the spring waters are still 
highly charged with carbonate of lime, and deposition is still going on. 

The map exhibits several areas in which the surface materials so 
obscure the underlying hard rock geology that it has not been deemed 
wise to represent the underlying formations in these areas. The 



36* GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

nature of the surface materials in these places is generally a complex 
consisting largely of rearranged landslide debris mingled with ordi- 
nary talus and wash, and not infrequently a growth of timber or of 
grass conceals the nature of the rock debris. 

It will be noted that the effect of nearly all of these recent agencies 
is to modify the form of the mountains existing before the glacial 
epoch and the beginning of the landslides by producing gentler forms 
of the ridges and by tilling np in some degree the various valleys. 



CHAPTER II. 

THE SEDIMENTARY FORMATIONS. 



By Arthur Coe Spencer. 



ALGONKIAN. 



Introductory statement. — The rocks which are here described as 
Algonkian occupy a small area in the center of the Rico Mountains, 
where they have been exposed by the deep erosion of the overlying 
Paleozoic strata. They comprise quartzites and quartzitic schists and 
are similar in every way to the series of rocks exposed in the upper 
part of the Animas Canyon and in the adjacent portions of the 
Quartzite or Needle Mountains, in which region they were represented 
on the Hayden map as "metamorphic Paleozoic," since it was the 
belief of the geologist who discovered them that these semicrystalline 
and indurated rocks had been derived from Paleozoic strata by the 
processes of metamorphism. That this view is entirely incorrect is 
now clearly established by the known relations which the unmetamor- 
phosed Paleozoic strata bear to the much older and much altered series 
upon which they lie in unconformable sequence. The basal member 
of the Paleozoic in the Needle Mountains is a quartzite which contains 
pebbles and bowlders of schist derived from the rocks upon which it 
rests, thus indicating conclusively that the metamorphic series existed 
in its present condition before the first Paleozoic beds were deposited. 

The sedimentary origin of the metamorphic rocks of the upper 
Animas Canyon was recognized by Endlich and has since been reaffirmed 
by Emmons 1 and Van Hise 2 , who have assigned them to the Algonkian, 
into which great geological group they naturally fall, since the Algon- 
kian is by definition made to include all recognizable pre-Cambrian 
rocks of sedimentary origin. 

Detailed description of the San Juan Algonkian is beyond the scope 
of the present paper, but since the phenomena presented at Rico are 
of themselves inadequate for drawing conclusions so far reaching as 

'Orographic movements in the Rocky Mountains: Bull. Geol. Soe. Am., Vol. I, 1890, p. 257. 
2 Pre-Cambrian rocks of North America: Bull. U. S. Geol. Survey No. 86, pp. 320, 325. 

37 



38 GEOLOGY OF THE EICO MOUNTAINS, COLOEADO. 

some it is desired to present, a few general considerations concerning 
the Algonkian maybe here given without stating data from which 
they are deduced. Those who are not familiar with the wider general- 
izations of geology will thus be enabled better to understand the sig- 
nificance which attaches to the extreme differences of rock character 
observed in the Paleozoic and pre-Paleozoic formations. 

The Algonkian rocks were originally formed as sediments at the 
bottom of the sea. just as the later stratified rocks were formed, and. 
like them, were made up of shale- and sandstones, probably with 
bands of impure limestone. From the time when their deposition 
was completed a very long period elapsed before the formation of any 
other strata of which we have knowledge, and during this period 
there ensued one of the greatest geological revolutions known, so 
widespread that it i- recognized over a large part of the world. In 
the course of this disturbance the strata, which had been piled up to a 
yen great but unknown thickness, were subjected t<> processes of 
physical and chemical change by which they were folded and dislo- 
cated and metamorphosed until their origin as sediments i- now fre- 
quently very much obscured. Some time during this period these 
formations were intruded by igneous rocks of different kinds, which 
have in manv cases also suffered metamorphism. After folding, the 

originally horizontal strata were left in variou- attitude-, for the 
mo-t pari greatly inclined. Subsequently the upturned fd^vs were 
planed down to great depth l>\ erosional processes ensuing upon con- 
tinental uplift. 

Relations of t/,, Rico Algonkian. — The correlation of the pre- 
Paleozoic rock- of Rico with the Algonkian i- based upon evidence of 
a structural nature and upon lithological resemblance to rocks of the 
Anima- ( 'anyon. 

In the northern pail of the Anima- region of pre Paleozoic rocks 
there is a general east-wesl trend, which IS will lirought out by a 
broad hand of quartzite that form- one of the most prominent (dements 
of the series. Standing at a high angle of inclination, this quartzite 
may be traced from the headwater- of the Rio Grande north of the 
Needle Mountain- westward across the Animas to the northern peaks 
of the West Needles, and theme to where they are covered l>v the 
flat-lying Paleozoic rocks on the west ride of Lime (reek. The dis- 
tance through which this structure i- thus known to persist is more 
than L2 mile-, and if continued for an equal distance in the -am.' 
genera) direction would carry the quartzites to Rico. It is, therefore, 
a fair inference that the Algonkian quartzite at Rico represents some 
part at least of the Anima- series, and that it probably corresponds 
directly with the prominent quartzite mentioned. 

The quartzites in both places are vitreous and for the most part 
medium or tine grained, though conglomerates are not wanting. 



spencer.] ALGONKIAN QUARTZITES AND SCHISTS. 39 

Along 1 the Silverton wagon road near Lime Creek the conglomerates 
arc very coarse, but nothing above medium coarseness is exhibited at 
Rico. In both regions cross bedding is well marked, and the color 
varies from white to red. Associated with the quartzite in the Ani- 
mas region and at Rico there are other rocks of undoubted sedimen- 
tary origin, such as quartzitic schists, and in the former localities dark 
indurated shales of more or less schistose structure. Also in both 
regions there are igneous rocks in the form of dikes usualh/ parallel 
with the bedding or structure of the schists. In many or perhaps 
most cases these igneous rocks have been metamorphosed with the 
rocks in which they are intruded. 

Description of the quartzites. — The Algonkian rocks, very imper- 
fectly exposed at Rico, consist of quartzites and quartzitic schists bear- 
ing small amounts of mica. The former are not distinguishable in 
character from other massive quartzites, to be described later, which 
are supposed to be of Devonian age; but their exposed thickness is 
greater, being more than 350 feet, probably at least 500 feet, while 
that of the younger formation is probably not more than 200 feet. The 
quartzites, as a rule, stand at steep angles. They are white or tinged 
with brown, with occasional red or rusty bands. The detrital mate- 
rial of which they are composed is almost entirely quartz, usually in 
small even-grained particles, but sometimes occurring in the form of 
pebbles less than an inch in diameter. The rock is completely indurated 
by the interstitial deposition of quartz, so that it is now glassy quartz- 
ite of the hardest kind, very resistant to erosion and to the miner's 
drill. Distinct partings between the beds of quartzite are nowhere 
observable in present exposures. However, the bedding or stratifica- 
tion planes may frequently be made out from a study of the massive 
quartzites where differences of grain are found or where cross bedding- 
is observable. Ripple-marked surfaces are also occasional^ seen. 
These structures, when taken with its constitution, are conclusive evi- 
dence of the sedimentary origin of the quartzite. 

Description of the schists. — The remaining Algonkian rocks may be 
termed schists, since they have a more or less distinct foliated struc- 
ture not due to original bedding but superinduced by metamorphism 
under stress. In these schists the stratification may be made out in 
some cases by differences in the character of adjacent bands, and to 
this feature the. foliation is generally, though no.t always, parallel. 
The direction of foliation does not vary greatly from east and west, 
and its position is nearly vertical wherever observed. 

The schists are dense bluish-gray rocks, the foliation being caused 
by the arrangement of very minute particles of biotite and actinolite, 
not recognizable to the unaided eye. A delicate luster is visible on 
the planes of easier fracture, but the schistosity is never very highly 
developed and the rocks often break readily across the structure with 
almost conchoidal fracture. 



40 GEOLOGY OF THE KICO MOUNTAINS, COLOEADO. 

Under the microscope the main mass of most of these rocks is found 
to be a fine-granular aggregate of feldspar and quartz. A little of 
the feldspar is visibly twinned according to the albitic law. The 
amount of orthoclase is difficult to determine on account of the small 
size of the grains. Biotite is always abundant in minute light-brown 
flakes, in excess of the more variable pale-green actinolite needles. 
Epidote is more or less irregularly abundant throughout the rocks, and 
is especially developed in veins or adjoining fissures traversing the 
rock. Small amounts of magnetite dust and apatite needles are 
present. 

In a few places the rock ha> quite clearly the character of a shearing 
product of an apparent porphyry in which there were phenocrysts of 
quartz and feldspar. There i- a slighl development of tourmaline in 
such rocks. The further description of these schists must be deferred 
until the large areas of similar rocks in the Needle Mountains have 
been investigated. 

Intruded into these schists, in general parallel t<> the structure, but 
sometimes crosscutting, are many thin dikes of a dark porphyritic 
rock. These are prominent on both sides of the river, bill have not 
been found in the Algonkian quartzites oor in any other rock than the 
schists; lience they are supposed to be very old intrusions, independent 
of the other eruptions of the region. This idea is substantiated by 
the shearing of some of the dikes. Stout prism- of hornblende are 
the only prominent ei\ -tab of the rock. There i- also much second- 
ary hornblende and epidote revealed by the microscope. The former 
subordinate feldspathic constituent i- so much crushed and altered 
thai the original character can not he determined. Plagioclase was 
probably predominant over orthoclase. 

Occurrences. The Algonkian rocks of the Rico Mountains all occur 
within an area of less than 90 acres, roughly estimated, but within this 
limited area the structure i- so complicated and the rocks are -<> much 
Covered that the relation- of adjacent exposure- can rarel\ he made 

out. On tin- account the relation which the schists and quartzites 
bear to each other ha- not been ascertained, for they occur in different 
fault blocks, and it is possible that the Devonian and Algonkian 
quartzites have been confused in some cases. 

There are -i\ separate areas of quartzite, and one of these, that 
south of Silver Creek, below Allyn Gulch, is certainly Algonkian, on 
account of its great mass; another, on the opposite side of Silver 
Creek is probably of that age, while the others have been provision- 
ally assigned to the Devonian. In the first place mentioned the 
quartzites have their greatest development. They are hounded on the 
east by a well-marked fault, shown in the Laxey mine: thence toward 
the, southwest they may lie traced for a quarter of a mile along the 
hillside, upon the slope of which their outcrops are to be seen between 



spenceb.] DEVONIAN ROCKS. 41 

the elevations of 0,200 and 9,500 feet, showing a continuous exposure 
at one, place to a thickness of 350 feet, though from the structure it 
is probable that a greater thickness is present. The strike and dip 
may be determined in this region, and while both are variable, the 
former is generally about N. 10°-30° E., and the latter is steeply 
toward the south of east. 

On the north, south, and west the boundaries of this mass of quartzite 
are not known, since they are covered by surface debris; but from the 
adjacent occurrences of porphyry belonging to the thick sill of New- 
man Hill it is almost certain that the quartzite is limited upon the 
south and west by faults, in the manner indicated on the map, while 
on the north it may connect underneath the valley wash with the 
quartzite upon the north side of Silver Creek. Within this latter 
area the rocks are very imperfectly exposed, except in local patches, 
but from these and from the data derived from tunnels and prospects 
it is definitely known that the northern limit is along the Last Chance 
fault, which has a nearly east-west course. The highest exposures are 
near this fault, at about 9,400 feet, and the quartzite can not extend 
much beyond this point, since green shales and sandstones are exposed 
at about the same elevation in the draw below the Alma Mater mine. 

DEVONIAN. 

General relations. — The strata which are here described as Devonian 
are believed to correspond definitely with a similar series which has 
been carefully studied in the Animas region, where the relations to 
the pre-Paleozoic and to the Carboniferous are well exhibited, and 
where a well-marked Upper Devonian fauna occurs. This series of 
the Animas Valley has recently been discussed in a paper entitled 
Devonian Strata in Colorado. 1 In this paper the name "Ouray lime- 
stone" was applied to the calcareous and fossiliferous member of the 
scries, the uppermost of three divisions which constitute the complete 
normal section below the Carboniferous. The middle member is a 
shale and the lower a massive sandstone or quartzite, frequently con- 
glomeratic in the lower part. Tn certain localities in the San Juan 
the quartzite was not deposited upon the Algonkian, and elsewhere 
both the quartzite and the shale are missing, in which case the lime- 
stone rests directly upon the pre-Paleozoic; but whenever the lowest 
member is present it is always followed in order by the other two in 
conformable sequence. It is possible that the shale and quartzite are 
pre-Devonian. 

When the massive marbleized limestones at Rico were noted at the 
base of the Carboniferous section it was at once suggested that they 
probably represented the, Ouray limestone, and when later evidence 

1 Arthur C. Spencer, Am. Jour. Sci., Vol. IX. 1900, pp. 125-133. 



42 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

of quartzites lying uhcomformably upon the upturned edges of the 
Algonkian schists was discovered, even though the supposed interven- 
ing shales were nowhere exposed, the identification was considered 
satisfactory; and finally, when a fossiliferous stratum belonging to the 
Carboniferous and characteristic of the lowest part of the Hermosa 
formation was found only a feet above the massive limestone the cor- 
rectness of the correlation was placed beyond question. 

For the Rico region it has been found necessary to group together 
all the members of this series and to represent them on the map by a 
single color, but since the series is represented in adjacent fields by 
two formations it is not desirable to give it a formation name, and it 
will therefore be designated by the name of the great time era to 
which it belongs. This usage is, however, entirely a matter of con- 
venience and must not be construed as indicating that the lower part 
of the series is surely Devonian, since there is still some room for 
doubt whether the quartzite may not belong to the Silurian. 

The aggregate thickness of the Paleozoic l>ed-< below the Carbonifer- 
ous in the San Juan region is about too feet as a maximum, and at Rico 
this figure is closely approximated, so far as imperf eel exposures allow 
of estimation and as indicated by the record of the boring made upon 
the Atlantic Cable claim in the town of Rico. This record, which 
was published in a paper upon the Enterprise mine by T. A. Kickard, 1 
is here given: 

ion of Atlantic Cable claim. 

Peet, 

Limestone 7 

Lead and zinc < >re 4 

Limestone 5j 

Lead and zinc ere 5 

Limestone 13 

White marble 20 

Zinc blende ere ;! 

Specular iron ore 18 

Limestone |;; 

Porphyrite 1 

Limestone 25 

Porphyrite 2 

Limestone 3 

Mineralized porphyrite :', 

Porphyrite 21 

Quartzite 1 70 

Total l^T 

The rocks penetrated evidently represent a thickness of strata 
somewhat less than the whole of the Devonian, since the top of the 
boring is below the top of the format ion. and the bottom of the 
quartzite was not reached. From surface exposures the thickness of 

'Trans. Am. Ii st. Min. Eng., Vol. XXVI, 1896, p. 917. 



spencer.] DEVONIAN QUAETZITE. 43 

the quartzite is believed to be about 200 feet, and perhaps i y ») feel 
should be added to the limestone series, so that the whole apparent 
thickness of the Devonian would be 393 feet, but from this 33 feet 
must be subtracted for intercalated igneous rock, and possibly half 
as much because of the inclined position of the strata, so that 350 feet 
may be taken as approximately the thickness of the Devonian. 

The quartzite. — The basal member of the Devonian is a massive 
quartzite, very dense and highly indurated. Its colors are dull yellow 
to white, with red and brown staining. The material of which it is 
composed is mostly quartz, and only slight variation in grain is 
observed, the mass of sandstone being fairly homogeneous. The 
stratification is sometimes discernible, though usually obscured by 
jointing and rifting. 

The Devonian quartzite is not distinguishable lithologically from 
that of the Algonkian except by its more regular bedding, but its lesser 
thickness and the unconformable attitude which it bears to the Algon- 
kian schists, together with its relation to the shales which overlie it in 
places, serve to separate it from the older formation in certain cases, 
though in others there may be doubt as to the correctness of assigning 
given exposures to one or the other of the quartzite formations. The 
best notion of the relation of the quartzite to the overlying limestone 
may be obtained by following along the west bank of the Dolores 
River from the Shamrock tunnel to the quartzite exposure above the 
Piedmont wagon bridge. Here the strata are all dipping southward, 
and though a portion of the beds are hidden it seems reasonable to sup- 
pose that the structure observed is not interrupted in any way, in which 
case the quartzite is shown in its proper relation below the limestone 
series, and probably separated from it by an unmeasured thickness of 
shales. The small outcrop of quartzite near the road just south of the 
smelter is also indicative of the same relations, but the only conclusive 
evidence, aside from the analogy between the supposed sequence at 
Rico and the known succession of strata in the Animas region, is that 
furnished by the record of the drill hole given above. From this 
record it appears that a thick body of quartzite actually does occur 
beneath the limestone at about the distance estimated from the surface 
exposures. Some doubt is expressed concerning the strata between the 
quartzite and the limestone, since the complete sequence is nowhere 
exhibited at Rico in a single section, nor were shales noted above the 
quartzite by the person who made the record of the Atlantic Cable 
boring. 

The quartzites which are so well exposed along the railroad on the 
north side of Silver Creek below the bridge have been referred to the 
Devonian on the map, but their age is somewhat questionable. They 
are evenly but rather massively bedded rocks, some bands being sep- 
arated by thin calcareous shale layers, and one notable coarse quartzite 



44 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

conglomerate stratum is exposed in the railroad cut. These beds strike 
N. 60° to 70° W., and dip about 30° in a direction west of south. This 
structure would carry them beneath the thin limestones and calcareous 
shales exposed by the South Park tunnel and penetrated by the Fate 
shaft. In the latter some of the thin limestones contain crinoid stems 
and unidentifiable shells, and appear to correspond to the basal strata 
of the Carboniferous, as known in the general Animas section and as 
actually seen on the west bank of the Dolores at Rico directly above 
the Devonian limestone. 

To consider the quartzites in question as Carboniferous involves (he 
assumption of a local development of pure quartzites below the ordi- 
nary base of the Hermosa formation, while the sandstones of that 
series are characteristically arkose in composition, containing much 
feldspar. To consider them as Devonian involves an explanation of 
the absence of the Devonian limestone which normally belongs above 
them. This might he accomplished by a north-south fault crossing 
between the Fate shaft and the quartzite exposures on the railroad, 
by which the limestone mighl be supposed to have been faulted up 
and removed by erosion. But in the South Park workings and appar- 
ently to the west of the possible line of such a fault very similar 
quartzites with a quartzite conglomerate are revealed beneath the 
Newman Hill porphyry sheet in about the position which the strata of 
the railroad cut would occupy if undislocated by such a fault as that 
hypothecated. It may be noted that a vein is exposed on the north 
bank of Silver Creek just above the South Park with the course 
assumed for this fault, but there is no means of determining I lie dis- 
location, if any. which has occurred on this vein fissure. 

The alternative explanation for the nonappearance of the Devonian 
limestone above the quartzites of the railroad cut is that it had been 
removed by erosion in this locality before (he deposition of the 
lowest Hermosa strata. Although no angular unconformity has been 
detected, as required by this explanation, the fact that Upper Carbon- 
iferous beds rest upon Devonian in the San Juan region and in the 
Dolores Valley at Rico shows that a great stratigraphic break does 
occur at this horizon, and this explanation is provisionally adopted as 
the most plausible under the circumstances. In discussing the faults 
of this part of Silver Creek (pp. 124—126) further details regarding 
this locality will be given. 

These quartzites are supposed to be limited on the east by a fault 
separating them from a wedge-shaped area between the Smelter and 
Silver Creek faults, within which there are almost no exposures. It 
has been assumed that the fault is not greal and that, the Devonian 
beds have been dropped in that wedge, a- is explained in another place 
(p. 125). 

The relations of the assumed Devonian quartzites to the schists may 



spencer.] DEVONIAN LIMESTONE. 45 

be studied near the northern limit of the Algonkian on cither side of 
the river, On the east side, near the Nora-Lily tunnel, quartzite IS 
seen only a few feet above exposures of the schist, and dipping about 
45° N. In this vicinity the schists stand nearly vertical, so thai ii is 
evident that the quartzite was deposited upon their eroded edges, and 
that it is, therefore, Devonian, in accordance with the relations seen 
in the adjacent Animas region. Similar conditions appear to exist on 
the ridge west of Piedmont, though outcrops of the two formations 
are not seen close together in this vicinity. Elsewhere at Rico the 
lower part of the quartzite is not exhibited. 

In both localities mentioned above, the schists underneath the 
quartzite are cut off on the north by an east-west fault, amounting to 
about 300 feet, by which the quartzite is dropped down, so that on the 
cast side of the river its top and a few feet of shales above it are 
exposed about 50 feet above the railroad track. This is the central of 
three known parallel fault fissures about 100 feet apart, each of which 
throws the formations down to the north. These seem to represent a 
splitting of the Last Chance fault. By' the northernmost the quartzite 
is entirely buried, while in the block between the southernmost and the 
Smelter fault the schists are raised an unknown amount. They arc 
exposed at the Futurity tunnel 400 feet above the river, but the rocks 
are covered above that, and it is not known whether the Devonian 
quartzite is present in this block or not. On the west side of the 
river, above Piedmont, the surface materials still more effectually con- 
ceal the structure of this complicated area. 

The exposures of the quartzite upon the Nora-Lily claim show a 
thickness of approximately 150 feet, but neither this nor the Atlantic 
Cable boring, which shows 170 feet of quartzite, gives the whole of 
the formation, since in the former the top is not seen and in the latter 
the bottom is not reached. It seems unlikely, however, that the total 
thickness is more than 200 feet. 

The lime-stone. — The Devonian limestone, as it occurs at Ouray and 
in the Animas region, is made up of massive beds of limestone separ- 
ated by thin intercalations of marl or shale. Certain thin bands are 
frequently quite coarsely crystalline, though this feature seems to be 
not due to metamorphism of the limestone, since the inclosing strata 
and the large mass of the formation is dense or semicrystalline lime- 
stone rather than marble. Fossils arc usually to be found in some' 
part of the series at any locality. 

At Rico the Ouray limestone has been greatly metamorphosed. 
When pure, it has the coarsely crystalline structure of marble, and 
where originally somewhat earthy it shows now the presence of vari- 
ous secondary silicates, such as garnet, epidote, pyroxene, and possi- 
bly vesuvianite. Any fossils which may have occurred in them have 
been destroyed, so that the original character of the limestone is 



46 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

entirely obliterated. This alteration is attributed to contact meta- 
morphism connected with the intrusion of the monzonite stock on the 
west side of the dome. Similar effects are seen in the baked and 
metamorphosed strata of the Carboniferous, where they lie adjacent 
to the monzonite upon Darling Ridge. A very good idea of this series 
of strata may be gained from a study of the exposures along the 
west side of the river between the Shamrock tunnel and the wagon 
bridge above. The limestone is limited above by baked shales and 
sandy limestone containing Upper Carboniferous fossils. The upper- 
most bed of limestone, which is very much metamorphosed, is about 
20 feel in thickness and is separated by a few feet of shales from a 
white crystalline bed about 25 feet thick, below which the strata are 
hidden for perhaps 60 feet, when another massive limestone is exposed, 
dipping, like the others, toward the south. The exposures opposite 
the bridge and just west of the road show thin bands of quartzite in 
metamorphosed shale, and these probably represent the lower limit of 

the limestone series, since massive quartzite is exposed a few rods 

toward the northwest in the bed of the river. The approximate 

thickness Of the limestone series, as estimated from these exposures, 
is 150 feet, though this figure would seem to be under rather than in 
excess of the true thickness. Other exposures of the limestone reveal 
neither the structure nor the thickness of the formation, but it is 
probable that the outcrops on the Atlantic ( able claim and at several 
tot openings above and to the east of the smelter belong to the upper- 
most of the limestone beds, since they show the same brecciated 
appearance that may be seen in the limestone at the Shamrock tunnel. 
In the boring of which the record is given on page 42, 120 feet of 
limestone were recognized, together with 20 feet of ore, which prob- 
ably represents the replacement of an equivalent thickness of lime- 
stone. "Porphyrite" is also recorded to a thickness of 33 feet. The 
thickness measured across the beds would be somewhat less than the 
above aggregate of 17:; feet, because the strata are not level but rise 

towai'd the north; but since the boring was started below the top of 
the limestone series, possibly 20 feet of limestone should be added, so 
that after subtracting the porphyry the thickness of the Devonian 
above the quartzite would be approximately 150 feet, which corre- 
sponds with the surface estimate given above. The structure exhib- 
ited by the limestone on the west side of the river, if continued toward 
the north, would carry the formation against the tongue of mon- 
zonite which cuts down the hillside south of the Montezuma mine. 
North of the monzonite it should again appear and fall successively 
toward the north, with the downward steps of the underlying quartz- 
ite. Unfortunately this slope is buried underneath surface debris, 
so that the actual relations can not be learned from such explorations 
as the geologist is able to command, and the presence of the limestone 



spencer.] CARBONIFEROUS ROCKS. 47 

must be taken as a suggestion rather than a conclusion. The same 
may be said for the probability of the limestone occurring above the 
quartzite on the east side of the river. In this case, however, its 
presence or absence could be determined by a small amount of exca- 
vation. 

Economic importance of 'the limestone. — The importance of the Devo- 
nian limestone at Rico is of course centered about it as an ore-bearing 
horizon, and speculation concerning it in this role has evidently en- 
gaged some of those who have been interested in the mining industry of 
this region. This point is discussed by Rickard in his paper upon 
the Enterprise mine, where the evidence then available was taken as 
distinctly against the presence of any " second contact' 1 beneath the 
"Newman contact" of the Enterprise and other mines of Newman 
Hill. The data upon which this opinion was based were mostly the 
records of shafts and borings which failed to show bedded ore bodies, 
or "blanket veins." It is evident from the structure exhibited by the 
geological map that the Ouray limestone has not been thoroughly 
explored on the lines where it is cut by the Smelter fault and minor 
fissures. But since it is highly mineralized in several places along 
the banks of the Dolores, carrying large bodies of heavy sulphides, 
it is seen to be a favorable horizon for the occurrence of ore bodies 
wherever it is cut by metalliferous veins. That it should be mineral- 
ized throughout its extent is, of course, entirely improbable, and it 
appears to be true that the sulphide bodies in it thus far developed 
are too low in silver contents to be of economic value. 

It has been assumed, as above explained, that the limestone is prob- 
ably absent in the vicinity of Silver Creek, above Rico, owing to pre- 
Carboniferous erosion, but it is to be hoped that future explorations 
will definitely settle this point. 

CARBONIFEROUS. 

The Cai'boniferous rocks of the United States have been divided 
into three groups: The Mississippian, or Eocarboniferous; the Penn- 
sylvanian, or Carboniferous proper, and the Permian; 1 the further 
designation of Permo-Carbonifei'ous 2 has also been used for strata 
which have faunal characters of an intermediate aspect. 

While all of these divisions, except the true Permian, are known 
within the limits of Colorado, the invertebrate fossils characteristic of 
the Pennsylvanian occur in the San Juan region within 100 feet or less 
of the Oura}^ limestone, and the existence of the Mississippian in that 
region has not as yet been demonstrated. 

In the Animas Valley and adjacent areas the Carboniferous strata 
have been divided into the Hermosa and Rico formations. The first 



H.S.Williams, Bull. U.S.Geol. Survey No. 80, 1891. 

: F. B. Meek, in Rept. U.S. Geol. Survey of Nebraska and adjacent Territories, 1872, p. 132. 



48 GEOLOGY OF THE EICO MOUNTAINS, COLOKADO. 

is correlated with the Upper Coal Measures because of its fossils, 
while the other is called Permo-Carboniferous, since its fossils are in 
part similar to those of the Carboniferous and in part like those of 
the Permian. 

HER OSA FORMATION. 
CHARACTERISTICS IN THE SAN JOAN REGION. 

Definition. — Occurring between I he Devonian limestone and the 
typical red beds, and sharply denned from each, there is a hetero- 
geneous series of locks which i- generally distributed in the San Juan 
region, where it reaches a maximum thickness of about 2,000 feet. 
It is characterized thro'ughout by a brachiopod fauna of Coal Meas- 
ure age, thus corresponding with the Missourian stage of the Penn- 
sylvania!! series as it occurs in the Mississippi Valley. Some of the 
more common characteristic fossils are Fusulina cylindrica, Productus 
semireticulatw, Productus nebra&ken&is, Productus cora, Spirifer 
cameratus, Chonetes mesoldbus. This group of strata will lie called the 
Hermosa formation, from the large creek of that name entering the 
Animas River in the Durango quadrangle. There are extensive expo- 
sures of the formation at many places in the drainage basin of this 
creek, the greater pari of which lies in the Engineer Mountain quad- 
rangle. 

General description. — LithologicaUy the Hermosa is composed of 
limestones. -hale, and sandstone, but all of these strata are more or 
less calcareous throughout. The limestones are of a blue-gray color, 
rather dense in texture, and usually very fossiliferous. They are fre- 
quently more or Less bituminous, sometimes so much so as to afford a 
distincl odor of petroleum when struck with a hammer. The shales 
vary from black bituminous clay shales, rather fissile, to sandy shales 
and sandstones of an olive-green color. The sand-tone- are also of a 
greenish color, and under the microscope are seen to bave an amor- 
phous green cement, the composition of which is unknown. The 
materials of the sand-tone- are usually feldspathic and frequently 
micaceous; they vary in grain from tine to coarse, and are sometimes 
conglomeratic. The formation bas a considerable distribution in the 
western part of the San Juan region, but throughout the area of it- 
occurrence it is not in general divisible, since individual beds and 
groups of strata change greatly in character from place to place, so 
that horizons cannot be definitely recognized in localities separated 
from one another by more than short distances. 

Animas section. — The strata of the Hermosa formation form the 
western wall of the wider valley of the Animas outside the canyon, 
from Hermosa Creek to the drainage of Cascade Creek, and thence, 
still northward, their outcrops may be traced nearly to Silverton. In 



spencer.] HERMOSA FORMATION. 4 ( .» 

this distance of 25 miles the variable and inconstant character of the 
formation is well exhibited. The f ossilif erous limestones which occur 

at the base just above the Devonian are found throughout this extent, 
but the strata above them change greatly from place to place. Near 
Hermosa Creek the lower part of the formation above the limestones 
is made up of green sandstones and shales with some bands of gypsif- 
erous shale; the middle and upper parts show f ossilif erous gray lime- 
stones in beds from 1 to 20 feet in thickness, interbedded with shales 
and sandstones. Northward from this region the limestones become 
more massive and the intercalated shales and sandstones less important, 
so that for some distance south of Cascade Creek the limestones of 
the middle section are very prominent, forming the upper scarp of the 
valley wall. The upper massive limestones extend westward nearly to 
Hermosa Park, and here the upper part of the Hermosa formation is 
seen to have some fossiliferous limestones within the shale and sand- 
stone series. The lower portion of the Hermosa is not well exposed, 
but important limestones are certainly not common in it above those 
which lie upon the Devonian. Gypsum has not been found north of 
the Durango quadrangle, though it may be present and undiscovered 
because hidden from view by surface debris. Between Lime Creek 
and Molas Lake the Silverton wagon road traverses the Hermosa for- 
mation, and in this vicinity it exhibits a distinct phase, since the blue 
fossiliferous limestones are less massive than to the south and are dis- 
tributed throughout the entire thickness of the formation. 

The variable character of the Hermosa, as shown in the preceding 
paragraphs, is indicative of the unity of the formation, and this is 
further borne out by the invertebrate fauna as a whole, which Mr. 
Girty finds it impossible to divide into subfaunas. No division can be 
made which will have other than local value. 

DESCRIPTION AND DIVISION OF THE RICO SECTION. 

General statement.— At Rico the Hermosa formation has about its 
normal development, since it reaches a thickness of 1,800 feet or more. 
It shows an unmistakable general correspondence to the Animas sec- 
tion, and in particular has a development similar to that in the adjacent 
portion of the Animas region, where the limestones in the medial portion 
of the formation are massive and conspicuous. At Rico, however, the 
gray or blue limestones are even more closely segregated in the middle 
third of the formation, and are of rare occurrence in the upper and lower 
portions. This is doubtless entirely a local facies of the formation, 
as may be inferred from the facts cited in the discussion of the Animas 
section, but it makes it possible to divide the Hermosa, as is shown at 
Rico, into three approximately equal parts, and this division will be 
followed in description. Upon the detailed geological map of the 
21 geol, pt 2 4 



50 GEOLOGY OF THE E1CO MOUNTAINS, COLORADO. 

Rico Mountains the upper member has been represented by a distinct 
pattern, in order bettor to exhibit the structure, but the two lower mem- 
bers have not been separated. This division is made simply as a matter 
of convenience, as there is no intention of raising the divisions to 
the rank or importance of formations. 

Lower division. — The lower division is about 800 feet in thickness, 
excluding the porphyry sills which have been intruded, between its 
strata. At the base and resting upon the Devonian limestone there 
are shales and Impure limestones which have been considerably baked 
and metamorphosed, but which may still be seen to contain abundant 
Upper Carboniferous fossils, and which correspond with similar strata 
occurring above the Devonian along the western side of the Animas 
Valley. Above this the rocks are green or grfty grits, or sandstones, 
alternating with gray shales and containing several beds of black shale 
and occasional thin impure limestones. The ore-bearing horizon of 
Newman Hill, known as the "contact." is associated with one of the 
black shales which occur- about 450 feet below the massive limestone 

series which forms the lower pari of the upper division of the Her- 

niosa. A bed of rock gypsum, sometimes reaching a thickness of 30 
feet, occurs locally above the black shales of the ••contact" series, 
and was probably more widely distributed originally, since wherever 
it has been seen there i- ei idence that it has been attacked by circulat- 
ing waters and in pari removed by Bolution. Above this is an interval 
of 250 feet which i- aowhere exposed to view, followed by 200 feet oi 
massive and flaggy sandstones constituting the uppermost strata of 
the lower division. 

Exposures of tfu lowerbeds.- Containing as it does the Newman Hill 
"contact," and at leasl one other ore-bearing horizon, knowledge of 
the lower division of the rlermosa formation at Rico becomes impor- 
tant in the study of the geological feature- of t he ore deposits. How- 
ex it. its strata are so much hidden by surface materials that, even 
with the aid of sections revealed in mine workings, only the most 
general idea of the sequence of strata has been gained. In what fol- 
lows it is intended to indicate as closely a> possible the position in the 
formation of the beds that are to be seen at the different localities 
mentioned. 

Underneath the superficial materials of varied origin which cover 
the lower slopes of the Dolores Valley, the lower part of the rlermosa 
formation occurs as an incomplete or interrupted elliptical band sur- 
rounding the town of Rico and the area of older locks outcropping 
just to the north of the town. 

The fossiliferous limestone marking the base of the formation is 
found above the Shamrock tunnel, where it- relation to the Devonian 
is apparent, but aside from this locality no other outcrops are known. 

Incomplete knowledge of the Devonian series, as well as of the 



spencer.] HEKMOSA FORMATION. 51 

Hermosa, and the extremely complicated structure in the valley of 
Silver Creek, precludes positive .statement as to the horizon of all the 
beds which outcrop in that vicinity. There is some reason for sup- 
posing that the calcareous shales exhibited north of Silver Creek, near 
the South Park tunnel, and which may be seen lying conformably upon 
the quartzite in the vicinity of the Fate shaft, belong between the 
quartzite and the limestone of the Devonian, but there are other facts 
which seem to indicate that they belong to the lower part of the Her- 
mosa. and though the matter is still in doubt, they have been repre- 
resented on the map as belonging to the upper formation. Concerning 
the black shales which are exposed in the railroad cut just south of 
where the Silver Creek wagon road crosses, there is less doubt. They 
belong to the lower part of the Hermosa. and with them must be 
placed the strata which have been revealed in the various tunnels and 
shafts in this vicinity. 

The character of the sandstones which occur in the lower 200 feet 
or so of the formation may be seen along the Enterprise road near the 
city limits, and in the strata traversed by the Hibernia tunnel on the 
south side of Silver Creek. In both places massive green sandstones 
and gray shales are to be seen. The only other exposures of Hermosa 
strata which are definitely known to lie below the horizon of the thick 
porphyry of Newman Hill are those in the lower part of Allyn Gulch, 
where several prospects have revealed sandstones and black shales. 

The thick porphyry sheet which has been intruded into the sedi- 
ments, and which has been mapped upon the north side of Newman 
Hill, reaches a thickness of about 500 feet, as indicated in the boring 
of the Skeptical shaft, and by the known occurrence above the shaft, 
but before reaching the west side of the river it seems to have thinned 
out or split into several sheets. For this reason it has been impossible 
to correlate the strata associated with porphyry at several places west 
of the river with those above the porphyry on Newman Hill. 

Immediately above the sheet there is a black shale, as seen at the 
New Year mine on Newman Hill, and other indications of black shales 
in this part of the section are seen in the materials which were raised 
from the shaft just north of the cemetery and in the tunnels and 
stopes of the Hunter mines, on the west side of the river. 

On Newman Hill definitely known strata of this lower division are 
exhibited in the workings of the Enterprise mine and in the shaft 
below the main level of the Union Carbonate mine. These sections 
show an alternation of gray or green sandstones and grits in beds 
from 8 to 20 feet thick, with gray shales of like development to an 
aggregate thickness of approximately 110 feet. Above this series at 
both places comes the ore-bearing complex composed of dark shales 
and limestones, and at its base there is another black shale about 15 
feet in thickness. This correspondence, taken with the general struc- 



52 GEOLOGY OF THE EICO MOUNTAINS, COLORADO. 

ture, is considered as strong- evidence that the ore horizons of the two 
mines are identical. The lower portion of the Union Carbonate shaft 
was not accessible at the. time the section was made, but it is reported 
that a third black shale was encountered at the bottom of the shaft. 
about 90 feet below the one mentioned above. Considering the nature 
of the strata which go to make up the formation, the black shales are 
apt to be the most constant horizons in the series, and while sandstones 
and other shales may lose their thickness and disappear, these maybe 
safely used for purpose-, of con-elation in so limited an area as the 
Rico region, when their relative position is once established. The 
exposures south of the Group tunnel, near the Newman mines, belong 
to this same general series below the ■•contact" shales. In several 
places in the Enterprise mine the rocks associated with the ore- 
bearing horizon are overlain by an irregularly intruded porphyry 
sheet from one to several feet in thickness. The black-shale series 
immediately below the porphyry has the constitution shown in the 
following section (from top downward), taken in the vicinity of Jumbo 
No. 2 vein near raise L3: 

Section in vicinity of Jumbo No. ; vein, Enterprise num. 

Ft. in. 

7. shale. Mack, somewhat brecciated 3 

<;. ■■( "(intact." consisting of gray pulverulent marly material, Bometimes struc- 
tureless ami sometimes stratified; frequently impregnated with silica, 

and varying in thickness from I to 2 feet 1 10 

5. Limestone, dark and impure, breaking with vertical fracture; locally known 

an "short lime" 1 5 

4. Black, fissile shale with occasional lenses of graj sandstone in the upper 

part •"> 

:i. Limestone similar to the "short lime." bul very black with gash veins <>i 

quartzite 1 <> 

2. Shale, dark gray 1 <; 

I. Sandstone 8 

T ital 22 3 

In parts of the Enterprise mine a bed of rock gypsum is found to 
occur above the black-shale series, sometimes reaching a thickness of 
30 feet. Its presence is noted also in the Rico-Aspen workings, where, 
at the bottom of the Silver (dance shaft, the following section (from 
top downward) was studied: 

n. ction m SUvt r Glance shaft. 

Ft. in. 

14. Gypsum, 2 to 4 feet 4 

13. "Contact" as in the Enterprise mine 1 2 

12. "Shortlime" 11 

II. Black shale 8 

10. Friable sandstone 1 1 

9. Shale and black limestone 1 <i 

8. Gray sandstone 9 

7. Black shales 1 2 



BERMOSA FORMATION. 53 

Ft. in. 
6, Black shale and Limestone in alternating bands from unc-half to 1 inch 

thick 1 8 

•">. Dense limestone of gray color with many gash veins 1 7 

4. Black shale 2 1 

:!. "Short lime," 1. lack 6 

2. Black shale 2 

1. Gray sandstone 20 

Total - - 39 4 

The occurrence of heavy beds of 'gypsum associated with black 
shales and block v bituminous limestones in the Animas region 1 in the 
corresponding - part of the lower Hermosa formation, together with 
the massive character of the gypsum rock as observed at Rico, is 
strong evidence for accepting the deposit as an original part of the 
formation rather than as of secondary origin through the action of 
sulphuric solutions upon limestone, as proposed b}' Rickard. 2 At 
Rico the gypsum is only locally present, though whether its absence 
is due to non deposition or to removal by solution can not be stated. 
Gypsum is perhaps the most soluble rock of ordinary occurrence 
aside from salt, and in the Rico- Aspen mine it is seen to be pitted 
and corroded, showing that circulating waters have been at work upon 
it there. If the gypsum was originally deposited throughout the 
region where the '•contact'' has been explored it is possible that the 
peculiar gray marly material, of which the latter is composed, may 
represent the insoluble residue of the gypsum which has been carried 
away. 

Above the "contact" for a distance of 250 feet, or thereabouts, the 
character of the rocks is nowhere exhibited at present, for though this 
interval has been penetrated by several of the shafts on Newman Hill 
there is no record of their sections. Above this the uppermost 200 
feet of the lower division of the Hermosa formation is composed almost 
entirely of green sandstones in massive and flaggy layers, but with 
only minor partings of shale. These sandstones are well exposed on 
the south side of the lower part of Deadwood Gulch, and again their 
upper layers are exposed below the faults in Deadwood Gulch and 
hack of the Laura mi ne house. They are also shown in part on the north 
side of Horse Gulch below the cliff's of Sandstone Mountain near the 
wagon road, and probably also in other isolated outcrops where their 
relations can not be recognized. 

Mi <l in! (I/i'/ximi. — The second division of the Hermosa is made up 
very largely of blue bituminous limestone, carrying many fossils and 
occurring in massive beds from 5 to LOO feel in thickness, separated 
by shales and sandy shahvs. In the lower part there are some inter- 
calated strata of green sandstone and green or black shales, and locally 
these continue through the series, separating beds of limestone which 

>Vide, p. 49. -T. A. Rickard, Trans. Am. \\\-\. Min. Eng., Vol. XXVI, p. 970. 



54 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

elsewhere lie close together. The medial or limestone member has a 
thickness somewhat in excess of 000 feet and is a prominent feature 
in the stratigraphy of the region. Its structure and general relations 
are exhibited in the illustration of Dolores Mountain (PI. Ill), where 
its white ledges are shown; and in Deadwood Gulch, whence it passes 
above Newman Hill with a gradual rise toward the north, as seen on 
PI. V. The massive limestones continue across AUvn Gulch, as shown 
on PI. IV, partly covered in the vicinity of the stream, but appearing 
on the east side of the gulch near the .Maggie trail and continuing 
until cut off by the Blackhawk fault, by which they arc buried to a 
depth of several hundred feet. Upon the surface the top of the scries 
is seen at the Blacksmith level of the Blackhawk mine, dipping rapidly 
from the northeast side of the fault toward Silver Creek. On the 
west side of the assure the limestones appear in the road near the 
Argentine shaft, and from this place occupy a hand between the Nellie 
Bly and Last Chance faults, in which the lines of stratification may be 
seen to rise rapidly across the steep hillside. On the west side of 
Nigger Baby Hill they are cut oil' by the profound displacement of 
the Nellie Bly fault, and in the Mock north of this fracture no outcrops 
of the formation occur. 

UponC.H.C. Hill the limestones are again present, occupying a 
position elevated with respect to the block immediately to the south, 
though the exact location and nature of the fault by which the strata 
have been raised have not been ascertained. In this region the rocks 
are not well exposed, being covered by large amounts of surface 
debris and obscured by surricial landslides. The bedded deposits of 
pyrite which have been encountered in several mines upon this hill 
probably occur within this limestone series. 

The massive limestones are well exposed by the cutting of the river 
south of Burns, and from this place rise rapidly into the cliffs of Sand- 
stone Mountain, where all but perhaps LOO feet of the series is exposed. 

The occurrence of these strata is illustrated on PL VI, which is a view 
of Sandstone Mountain from the east. The limestones are here less 
massive than in the Eaceof Dolores Mountain, seldom reaching a thick- 
ness of 25 feet, as opposed to beds of uninterrupted limestones 60 to 
100 feet in thickness in the latter place, but the upper limit of the series 
is definitely recognizable in both places at the base of a homogeneous 
bed of light-colored calcareous sandstones and marls nearly LOO feet in 
thickness. The following section of the strata exposed in Sandstone 
Mountain, from near the top of the Hermosa to the lowest exposures 
not far from the base of the central division, was studied by Mr. Cross. 
In the saddle of the long ridge above the 10,400-foot level, the base of 
the Rico formation crosses, with its characteristic fossil limestones, 
below which the Fusulina layer is exposed: but below this the con- 



bpbncee.] SECTION OF THE HERMOSA FORMATION. 55 

tinuity of the section is broken by a fault, raising the strata toward 
the south. The section begins below the fault. 

Section I from top downward} in Sandstoni Mountain. 

54. Coarse grit, rather thinly laminated 10 

53. Dark-red sandy shale, with very smooth, undulating partings 5 

52. Sandy limestone, containing nodules anil lenses of pure limestones 5 

51. Massive sandstone, gray in the lower part and red above; this stratum 

forms the knoll above the 10, 450-foot contour 20 

(il. Porphyry, 25 feet.) 
50. < rray and green sandstone of medium coarseness, with rather distinct bed- 
ding-, occurring in two bands separated by a shaly parting 30 

(c. Porphyry, about 30 feet.) 

49. Massive grit 8 

48. Red, sands', and micaceous shale, weathering into thin flakes 5 

47. < xrit and conglomerate; the upper 5 feet is of medium grain and laminated, 
while the lower 15 feet is massive, and it is made up of quartz and ortho- 

clase with quartzite and granite pebbles distributed through it 20 

46. Shaly sandstone with calcareous nodules in the upper part 6 

45. Massive gray sandstone, grading upward into No. 46 18 

44. Dull-red shaly sandstone 3 

43. Massive gray sandstone, grading upward into No. 44 12 

42. Calcareous shales and sandstones of a red or pink color, containing nodules 

or lenses of gray, often bituminous limestone 35 

41. Massive sandstone or grit containing some pebbles 7 

40. Calcareous shales and sandstones of a light color 20 

39. Fine and even grained sandstones of a gray-green color, with occasional 

shaly partings 25 

38. Black shales, mostly very thin bedded and fissile, containing hands of 
bituminous limestone, which, when pure, is of a rough, coarse texture, 
but when sandy is hard and laminated; the limestone layers contain 

crinoid stems and shells 77 

37. Gray or green massive sandstone, very hard and of medium grain _ _ _ 6 

36. Sandstones and sandy shales 3 

35. Light-gray sandstone and calcareous shale in alternating beds, from a few 
inches to 2 or 3 feet in thickness and containing some layers of nodular 

limestone 32 

34. Sand y shale of a hematite-red color 15 

33. Greenish-gray calcareous sandstone of medium-coarse grain, forming a 

prominent hut thin-bedded series 22 

32. Blue-gray limestone; somewhat shaly in the lower part, hut massive above 

and richly fossiliferous throughout 7 

31. Coarse-grained sandstone with a calcareous cement 12 

30. Calcareous and bituminous sandstone 3 

21). Blue bituminous limestone, rather coarsely crystalline 3 

28. Greenish-gray massive sandstone of medium-coarse grain, and having a 

calcareous cement 13 

27. Black, carbonaceous, somewhat sandy shales, containing thin bituminous 

limestone hands, some of which contain many fossils 40 

26. Green or gray sandstone of a fine-grained, close texture 1 

25. Dark sandy and calcareous shale : 5 

24. Light-gray thin-bedded sandstones, calcareous in part 20 

23. Sandy and calcareous shales, partly 'lark and parti) light-gray'; some of 

the strata contain many hrachiopod shells 24 



56 GEOLOGY OF THE EICO MOUNTAINS, COLORADO. 



22. Blue-gray massive and fossiliferous limestone 3 

21. Calcareous shales and thin-bedded sandstones of a light-gray color, form- 
ing an indivisible series 95 

20. Gray massive limestone, containing corals (S 

(b. Porphyry, about 75 feet.) 

19. Rather thin-bedded limestone made up very largely of crinoid stems, but 

containing also some other fossils 15 

18. Green-gray or reddish sandstone, massive and calcareous in the upper 

pair and alternating with sandy shale near- the base 3(> 

17. Blue limestone of a dense texture 3 

16. Greenish-gray dense, but thin-bedded sandstone 35 

15. Limestone, massive in the lower part, but wavy bedded near the top; con- 
tains many crinoid stems 7 

14. Green fine-grained sandstone, rather thin lied, led. but forming a promi- 
nent outcrop 16 

13. Blue-gray limestone, rather massive, bul wavy bedded near the top; this 

layer contains man] crinoid stems 12 

12. Medium to fine-grained sandstones, for the most part thin bedded or 

shaly. but with some massive layers 30 

11. Blue or dark gray fine-grained sandstone, very thin bedded or shaly 4ti 

10. Blue-gray fossiliferous Limestone, made up of wavy layers 2 to 3 inches 

thick 14 

i ii. Porphyrj , 5 E< 
9. < .ra\ . medium-grained and thin-bedded sandstone: very friable in part . . 20 
8. Shaly sandstone with a calcareous cement having an irregular fracture; 

color, usually dull red. but sometimes greenish 21 

7. Massive gray sandstone, arkose in character and of medium coarse grain. 3 

6. Dull-red sandy shale 3 

5. Light-graj limestone of a dense texture, with a few crystals of calcite dis- 
seminated throughout the mass; this stratum is nodular in the lower 

part, and to some extent throughout its thiekne-s, and it contains a few 

corals 2 

4. Sandstone, partly laminated and partly massive; the laminated portions 

d, while the more massive portions are green 10 

36. Limestone, rather thin bedded, Occurring in wavy hands from a few inches 
to a foot in thickness; this stratum has a concholda] fracture which 
passes through the shales and crinoid stem- contained in the limesto 
under the action of the weather it- surface-.- become rough and prickly. 20J 

3a. Similar to 3&, but in addition tin- weathered surface shows a peculiar mot- 
tling because of dense part- outlined by dark curved lines of coarsely 
crystalline calcite, which in weathering stand out as projecting ridges.. -•'. 

2. Purplish-red shaly sandstone; this stratum is in part bidden, but seems 
to be made up of a fine-grained, crumbling calcareous shale in which 
limestone nodules are also present 15 

1. Blue-gray limestone, massive in the lower part, but rather thin beddt d in 
the uppermost 3 feet, where it carries lenses of chert; tiri.- limestone 

contains crinoid stems and a few brachiopod shells; it weathers with 

a rough surface 21 

T( >tal 938 

The medial division of the Herraosa includes all the strata of the 
above section from the base up to and including No. 20 of the section. 
The strata above No. 20 belong to the upper division of the formation. 



bpencjeb.] UPPER DIVISION OF THE HERMOSA. 57 

111 Papoose Creek limestones are well exposed, and in the vicinity 
of the Puzzle mine are to be seen in the mine workings and also in 
surface exposures. Farther to the west, upon the south side of Horse 
Gulch, the limestones have been baked and metamorphosed and at 
present show a marbleized condition and the presence of pyroxene and 
garnet. The exposures in this region are very poor, but the rapid 
rise of the strata toward the south may be made out, and enough may 
be seen to show that this series runs around into Iron Draw, connect- 
ing with the exposures which may be seen in the cliffs in the vicinity 
of the Zulu Chief mine. In this region they are also locally metamor- 
phosed, undoubtedly by the stock of monzonite of Darling- Ridge. 
Elsewhere on the west side of the river the main mass of limestone is 
nowhere exposed in place, unless the blocks which occur on the river 
bank south of the Silver Swan mine are outcrops in situ. However, 
there is strong evidence that they form a part of a large landslide mass 
which has come down from the slopes above. The series is without 
doubt present under all the surface debris in the slopes south of 
Sulphur Creek, but so deep is the mantle of loose material that all 
the formations are effectually hidden as far to the south as Burnett 
Creek. 

1 1> per division. — The upper division of the Hermosa, which is mapped 
separately, contains some bands of limestone similar to those of the 
medial division, but they are thin and unimportant in comparison. 
Its strata are mainly black and gray shales alternating with green grits 
and sandstones. Occasional reddish sandstones are observed, and two 
black shales are present in the lower third of the division. The top of 
the upper division, and of the Hermosa formation as a whole, is well 
defined from the base of the next higher formation. The topmost 
member consists of about 30 feet of fine-grained mica-bearing green 
shales, immediately above which comes a red, sandy, fossiliferous lime- 
stone of the llico beds. At the base of this shale a band of blue lime- 
stone, usually from 6 inches to 1 foot in thickness, is always present, 
and this stratum is characterized by the minute spindle-shaped shells 
of Fusulina cyli/ndrica, a fossil which is not known to occur above the 
Pennsylvanian Carboniferous. The upper portion of the Hermosa is 
of less importance from an economic standpoint than either of the 
lower members, but in order that the basis of separation of the Her- 
mosa and llico formations may be easily studied upon the ground, some 
localities may be mentioned where the Fusulina limestone is to be seen, 
and where its relations to the fossil-bearing strata of the higher forma- 
tions may be observed. 

In the steep slopes of Dolores Mountain on the west the Fusulina 
layer may be seen at various places just below the change of color 
from green to red which marks the line between the upper Hermosa 
and the Rico strata. In this region the fossiliferous hands of the 
latter formation are also well exposed. 



58 GEOLOGY OF THE KICO MOUNTAINS, COLORADO. 

The following section of the upper beds of the Hermosa formation 
was studied on the south side of the gulch back of the Laura shaft, on 
the west slope of Dolores Mountain. The top is just below the lowest 
fossiliferous sandy limestone of the Rico formation. 

Section [from top downward) on Dolores Mountain. 

Feet. 

26. Green fissile shale 6 

25. Green micaceous shale, irregularly bedded, sparingly fossiliferous, with 

crinoid stems 10 

(6. Porphyry, 10 feet.) 

24. Crumbling green shale, containing very few fossils 15 

23. Fusulina limestone J 

22. Green shale 2 

21. Crumbling green shale 4 

20. Coarse arkose sandstone, cross bedded, gray 6 

19. Red sandstone ami earthy limestone and calcareous shale 10 

18. Dark-red sandstone, micaceous, containing nodules of black limestone... 6 

17. Red and gray crumbling shale 9 

16. Red sandstones, micaceous 5 

15. Arkose sandstone, micaceous, containing some small pebbles, rather coarse 

as a whole, gray 15 

14. Micaceous sandstones, grading into gray and reel earthy limestones 15 

13. Sandstone, micaceous and Baggy, red 25 

12. < rreen shale-, fissile in part, also micaceous; near the bottom of the series 
there is a thin bituminous limestone, eon niy composed of commi- 
nuted shells 22 

11. Arkose sandstone, gray 15 

[a. Porphyry.) 

10. Red shaly sandstone and gray conglomerate alternating 40 

9, i Iray earthy limestone and micaceous sandstone 20 

S. Series of red and green sandstones, SOmewhal arkose, with a 4-foot sandy 

limestone, 25 feet from the top 35 

7. Not well exposed, but probably green Carboniferous sandstone 25 

ii. Black shale, with fossiliferous limestones near base, containing Produetus 

and other fossils 30 

5. Limestone, gray, somewhat sandy, contains much comminuted shell 

material 3 

4. Sandstone, line grained, red in tic lower part 6 

3. Limestone, earthy, more or less marly, not distinguishable from the lime- 
stone of the Dolores formation 12 

2. Covered, probably red, micaceous sandstone 10 

1. Sandstone rocks of a medium and uniform grain, cross bedded, green 20 

T< »tal 354 i 

Below this section the strata are displaced by a fault, and can not be 
identified in their relation to the beds exposed above. 

The characteristic strata at the top of the Hermosa may be seen 
again in the lower part of Uncle Nod Draw, where they serve as an 
accurate guide in determining the amount of faulting upon the Uncle 
Ned fissure, which is a direct extension of the Blackhawk fissure. 
Thev are also to be seen in the high dill's northeast of C. II. C. Hill and 



spencer.] HERMOSA FOSSILS. 59 

just north of Marguerite Gulch. They have been found on the ridge 
west of Papoose Creek, but have not been discovered in the region 
between this and the ridge north of Burnett Gulch. In this last place 
they are very poorly exposed, but cross the ridge in the vicinity of 
the 10,600-foot contour. On the south side of Burnett Creek they are 
again exposed. The line which has been drawn on the map to repre- 
sent the top of the Hermosa formation may be taken as a guide in 
searching for these characteristic horizons. 

A typical section of the upper division of the Hermosa as it occurs 
in Sandstone Mountain lias been given on page 55, but this section does 
not include the highest layers of the formation. Possibly 75 feel of 
strata may have been let down by the fault which crosses the ridge 
south of the base of the Rico formation, and no good outcrops could 
be found to show the local character of this part of the section. 

FOSSILS AND CORRELATION. 

Organic remains are numerous and well preserved in the Hermosa 
formation. By far the larger number are brachiopods, though gas- 
teropods occur, and also the characteristic foraminifer Fusulina cylin- 
drica. Most of the species are identical with forms occurring in the 
Missourian stage of the Carboniferous of the Mississippi Valley, 
which corresponds in point of age with what is commonly known 
as the Coal Measures. The same assemblage of organic forms is 
found at various places in Colorado. In the Gunnison region similar 
fossils are found in the Weber and Maroon formations, as described 
in the Anthracite-Crested Butte folio of the Geological Survey, show- 
ing that the Hermosa comprises the former and part of the latter 
formations. It also probably represents all of the Aubrey series of 
the Plateau and Grand Canyon regions, though conforming more pre- 
cisely with the description of the upper portion than of the lower. 

The detailed studies which have recently been made of the sedi- 
mentary rocks of the San Juan region have led to a grouping of the 
Carboniferous and of the red portion of the Juratrias quite different 
from that employed by the Hayden Survey. Reference to the Hay den 
Atlas of Colorado will show that the strata between the Devonian and 
the Jurassic sandstone (corresponding to the La Plata) were mapped 
as Middle and Upper Carboniferous. The mapping of the former 
division corresponds in general with the occurrence of the Hermosa 
formation, leaving the latter as the equivalent of the Rico and Dolores 
formations. 

RICO FORMATION. 

Definition. — It is here proposed to apply the name Rico to a forma- 
tion assumed to be about 300 feet in thickness, occurring between the 
Hermosa or characteristic Pennsylvania!! Carboniferous and strata 



60 GEOLOGY OF THE KICO MOUNTAINS, COLORADO. 

assigned at present to the Trias of the San Juan region— the Dolores 
formation. It is made up of sandstones and conglomerates with inter- 
calated shales and sandy fossiliferous limestones. In its lithological 
features it resembles the strata immediately above it, but its fossils 
are distinctly of Paleozoic age. and while many of its forms are com- 
mon to the Hermosa formation, others are of Permian type, so that 
it seems proper to designate its age Permo-Carboniferous. to indicate 
that it is transitional between these divisions of the Carboniferous 
system. In the Rico region the formation is conformable upon the 
Hermosa and is followed by the Dolores with seemingly perfect paral- 
lelism of stratification. The fauna as a whole has an aspect quite 
different from that of the Hermosa, since it is largely composed of 
lamellibranchs as opposed to the brachiopod assemblage of the lower 
formation. The boundary between the Rico and Dolores formations 
is at present entirely artificial, being based upon the highest known 
occurrence of the Rico fossils. The former is made to include only 
strata characterized by the Rico fauna, while the latter comprises the 
apparently unfossiliferous medial portion of the Red beds together 
with the upper part, of known Triassic affinities. The actual age of the 
unfossiliferous \lrd beds is thus left in doubt; they may eventually 
prove to be either Permo-Carboniferous, true Permian, or Trias. 
They correspond to what has been called Trias throughout the Rocky 
Mountain province. 

Disc,,,-, ,■ i j <>f th, -formation. — The Rico formation was lirst recog- 
nized as distincl from the \U'(\ beds which lie above it during the field 
season of 1898. Its fossils were firsl collected in the vicinity of Her- 
mosa Park, and were afterwards found in the lower part of Scotch 
Creek, a tributary of the Dolores at I he southern base of the Rico 
Mountains. At this place it- well exposed strata are abundantly I'os- 
siliferous, and from them were collected the larger part of the material 
from which the age relation- have been determined by G. II. dirty. 
The Scotch Creek section is given on page 62. 

Description. -The general characteristics of the Rico formation in 
the vicinity of Rico are, first, it- calcareous nature, in which it resem- 
bles the strata above and below; second, the very arkose character 
and the coarseness of its sandstones, in which re-pect it differs from 
the Hermosa and resembles the Dolore.-: and. third, its chocolate or 
dark-maroon color, which contrast- sharply with the gray or green of 
the Hermosa and which is more or less distinct from the bright ver- 
milion of the Dolores. Locally, through lnetamorphism, the deep-red 
color has been changed to green, a- -een in the cliff exposures north 
of Silver Creek, in the vicinity of the Uncle Ned Draw, and in the 
cliffs exposed on the northern slopes of Dolores Peak. 

The bulk of the formation is made up of sandstones and sandy shales 
composed of such materials as are derived from the disintegration 



bpenckb.] RICO FORMATION. 61 

of granite. The sandstones are mostly course or conglomeratic, 
always showing grains of fresh feldspar mixed with mica Hakes 
and quartz. When conglomeratic the pebbles are chiefly of schist and 
quartzite. The coarser sandstones are usually cross bedded and occur 
in massive beds from 2 or 3 to 25 feet in thickness. Some of the 
coarse sandstones are of very much lighter color than the mass of the 
formation. When tine grained the sandstones are usually somewhat 
laminated and pass into sandy shales. The shales, aside from the 
sandy varieties, are of two kinds — the tine-grained, unlaminated, red, 
marly beds, similar to those of the Dolores, and the equally tine- 
grained laminated clay shales of a green color. 

Intercalated with the sandstones and shales, which are for the most 
part very calcareous throughout, there are several beds of impure 
limestone, some as earthy gray, sometimes nodular bands associated 
with the marly shales, and others as sandy limestone of a red color in 
strata from 6 inches to 2 feet in thickness. The latter and a 0-inch 
layer of limestone,, which was taken as the upper limit of the forma- 
tion in Scotch Creek, are very fossil if erous. The sandy fossiliferous 
bands have a characteristic appearance wherever they are found, since 
the fossils are preserved in white calcite, in sharp contrast to the red 
matrix of calcareous sand. They are found in the lower third of the 
formation, and while some of them are of local development and may 
be seen to grade both vertically and horizontally into the sand rock 
with which they are usually associated, at least one band is known to 
be persistent in the Rico region, and its equivalent has been recog- 
nized in those parts of the San Juan where its horizon has been studied. 
This fossiliferous band thus becomes diagnostic of the Rico formation, 
and is especially valuable in the study of the stratigraphy of the region, 
since it occurs within a feet feet of shales which contain Hermosa fos- 
sils. At Rico its position varies little from 30 feet above the Fusulina 
limestone of the Hermosa formation, from which it is separated by 
green micaceous shales carrying shell fragments and crinoid stems, 
and is thus a reliable guide in defining the two formations. The for- 
mation is without any definite limit at the top, since the rocks which 
follow immediately above the highest known fossil-bearing beds are 
similar in every respect to the strata of the lower series; nor is it pos- 
sible to apply the change in color as a criterion, except in a very 
general way: so that it has been found necessary to assume the thick- 
ness of the format ion as equal to the greatest known thickness between 
the base and the uppermost fossils. In Scotch ( 'reck the thickness on 
this basis would be 237 feet; on the north side of Silver Creek, near 
the Uncle Ned Draw-, it would be about the same, but on the south 
slope of Nigger Baby Hill it is more than 300 feet. In drawing this 
upper boundary on the map the formation lias been represented as 
about 325 feet in thickness. 



62 GEOLOGY OF THE EICO MOUNTAINS, COLOEADO. 

The measured section taken in the lower part of Scotch Creek, 
which is given herewith, illustrates the features brought out in the 
foregoing description: 

Section (from top doionward) of the Rico formation on Scotch Creek. 

Feet. 
22. Two fossiliferoua limestones, each 6 inches to l foot thick, and separated 

by about 3 feet < if green shale 4 

21. Poorly exposed slope, containing several thin beds of light-colored sand- 
stone, and in the upper part red sandy shale 20 

20. Arkose sandstone, rather coarse, and containing some pebbles up to 1J 

inches in diameter; pink 7 

19. Shale and thin-bedded sandstone 7 

18. Earthy limestone, unfossiliferous 1 

17. Shales, forming a slope with a few thin bands of line-grained sandstone; 

gray, green, and red 18 

It;. Mas-ivc arkose sandstone of a red color, quite conglomeratic in the middle, 

and resting upon a pink arkose conglomerate 2 feet thick 22 

15. Crumbling shale, containing nodules of gray limestone; red 20 

14. Sandy fossiliferoua Limestone; red 2 

13. Series of variable sandstones; in the upper part the sandstone is thin bedded 
and alternates with shale; in the lower part the sandstones are of coarser 
grain; one layer showed probable worm borings; dark red, except for a 

few gray si reaks 27 

12. Gnarly limestone, earthy in the upper part 4 

11. Friable sandstone and thin shale layers; dark red 15 

10. Thin-bedded sandstone, passing downward into massive arkose sandstone 

and conglomerate; reddish 16 

it. ( 'rumbling shales of a dark-red color, containing band of gnarly limestone 

in the middle part 10 

s. Arkose sandstone and conglomerate, pink or white. 2 to :! feet 3 

7. Micaceous calcareous sandstone and shining shales; dark red 3 

6. Fossiliferoua limestone, 1 foot to 15 inches 1 

5. Micaceous sandstone, showing poikilitic structure, and containing some 

fossils; the upper pari is rather massive; the lower part rat her thin bedded 

and shaly 9 

4. Fossiliferous limestone, is inches to 2 feet 2 

3. Heavy micaceous sandstone .if alternating red and gray colors, sometimes 
variegated; this contains a 12-inch layer of reel, sand)-, fossiliferous sand- 
stone about 8 feet from the base, but grades up to a similar fossiliferous 
band 18 inches thick into a reddish, somewhal shaly sandstone about 10 

feet thick 20 

2. Micaceous sandy shale of a dark-red color 20 

1. Sandy limestone, very fossiliferous. grading downward into gray (lags 6 

Total thickness exposed 237 

Immediately below the lowest fossiliferous limestone there are 
micaceous calcareous shales, carrying a few shell fragments, in a thick- 
ness of 25 feet and representing the topmost beds of the Hermosa 
formation. 

Local distribution. — The Rico formation is shown on the map as a 
band encircling the Hermosa formation except in those portions of 



spenckb.] RICO FORMATION. 63 

the area where it is hidden by surface debris. The base of the scries 
is easily recognized wherever it outcrops; it may be seen on the ridge 
south of Ueadwood Creek at the 10,450-foot contour, and again appears 
in the stream bed at the It). 550-foot contour, and again upon the south- 
western shoulder of Dolores Peak, and from here may be traced with 
practical continuity to the ridge west of Allyn Gulch. Its position 
was accurately located on the east side of the knob between the forks 
of Allyn Gulch, but just east of this it is buried by the Blackhawk 
fault. However, it is again discovered in the vicinity of the Leila 
Davis mine, dipping steeply to Silver Creek, and appears from under- 
neath the talus just east of Uncle Ned Draw at 10,025 feet. Here the 
relations of the Fusulina layer and the sandy limestones at the base of 
the Rico formation are well shown on the east side of the ravine in the 
lowest exposures. Upon the west side they are also discovered about 
85 feet higher up, having been raised by the fault which follows the 
ravine. In this vicinity there are two fossil limestones less than a 
foot in thickness at the base of the Rico. The upper has the usual 
sandy character and forms part of a sandstone ledge; the lower, how- 
ever, is quite free from sand and occurs as a distinct and very fossil- 
iferous stratum in green sandy shales. Of these last there are from 3 
to 5 feet between the two limestone bands and 35 feet underneath the 
lower and above the Fusulina layer. The boundary may be traced 
across Nigger Baby Hill, rising gradually until cut off by the Nellie 
Bly fault near the nose of the ridge. On the west side of the hill its 
presence is marked by the outcrop of the Hope vein, which, with the 
other veins that outcrop upon this stope, lies in the line of the stratifica- 
tion of the rocks. The proof of this statement may be seen in the occur- 
rence of Rico fossils above the Hermosa beds near the Hope tunnel, where 
the apex of the vein is about 30 feet above the tunnel level, and in the 
fact that the Hope vein has been traced by the writer by means of the 
Hope and Phoenix workings from its outcrop to the Nellie Bly fault 
and found to lie in the line of stratification all the way. A short dis- 
tance north of the Hope mine the rocks are hidden by surface materials 
and the Rico formation is not again recognized until the cliffs north 
of C. H. C. Hill are reached. Here the basal strata may be clearly 
seen, cut by several minor faults and descending steeply to the river, 
where they are again well exhibited in Marguerite Gulch. Not 
actually exposed on the slopes above Burns, they reappear on the flat 
ridge of Sandstone Mountain above the 10,400-foot contour, and again 
on the ridge west of Papoose Creek at an elevation somewhat lower. 
In the western half of the mountains they are not again recognized 
north of the southeast ridge of Expectation Mountain, where fragments 
were found upon the surface on the southern slope above 10,500 feet. 
On the south side of Burnett Creek the base of the formation is found 



64 GEOLOGY OF THE EICO MOUNTAINS, COLORADO. 

about 150 feet above the lowest thick porphyry sheet, which position 
it is assumed to hold to the limits of the area represented by our map. 

As thus traced and as exhibited on the map. the Rico formation 
brings out the main structural features of the Rico Mountains, and in 
several instances has been the key to the measurement of the faults 
which cut the strata. So far as now known, the only place where the 
formation has been the country rock for valuable mineral veins is 
upon Nigger Baby Hill, north of the Nellie Blv fault. 

Correlation. — That strata related to the Permian of the Mississippi 
Valley should be found in the southwestern part of Colorado might 
naturally have been expected from the occurrences of such strata in the 
surrounding regions. Fossils of Permian affinities were found by the 
geologists who accompanied several of the military and railroad expe- 
ditions which traversed the Rocky Mountains and adjacent regions 
from the early fifties on. From New Mexico Permian fossils were 
reported as early as L858 by B. F. Shumard. 

In 1875 Mr. G. K. Gilbert, 1 in a description of the Paleozoic forma- 
tions of the Plateau region, noted the occurrence in the 1 upper part 
of a series of strata having Uppei Carboniferous affinities of certain 
fossils which suggested the Permo-Carbonif erous age of the rocks in 
which the}^ occurred. 

In 1878 Mi'. Clarence King reported the occurrence of Permian 
strata in the Wasatch and Uinta mountains, and represented the Per- 
mian on the maps accompanying the Fortieth Parallel Report. 

Iii L880 and later, in L885, ( 'apt. (now Major) C. E. Dutton :; described 
rocks with Permian affinities in the Plateau region, and at Fort Win- 
gate. New Mexico. He was able to trace these strata, which he 
describes as Permo-Carboniferous, over the greater part of the Pla- 
teau region, to identify them with the Shinarump conglomerate, which 
had been previously described by Powell, and to establish a direct 
stratigraphic correlation with the beds which King had called Permian 
in Utah and Wyoming and northwestern Colorado. At this time Dut- 
ton called attention to the probability that the Pernio ( aiboniferous 
would eventually be found in the southwestern part of Colorado. 

In 1880 Mr. C. D. Walcott, 1 in a paper entitled The Permian and 
Other Paleozoic Groups of the Kanab Valley. Arizona, described as of 
Permian age a series of gypsiferous and arenaceous shales and marls, 
with occasional limestone bands. The group was divided by both 
stratigraphic and paleontological evidence into an Upper Permian and 
Lower Permian series. The upper series was considered, from its 
fossils, to be of true Permian age; while the lower series has a fauna 
containing certain Carboniferous types mixed with the Permian. This 

1 U. S. Geog. Surv. W. One hundredth Mer., Vol. [II, Geology, 1875, p. 177. 

2 U.S. Geol. Expl. Fortieth Par., Vol. 1, 1878, p. 343. 

SBull. Philos. Soc. Washington, Vol' III, 1879, p 67, Sixth Ann. Rept. U.S. Geol. Survey, 1885, p. 134. 
<Am. Jour. Sci., 3d series, Vol. XX, pp. 221-22.'.. 



AGE OF THE RICO FORMATION. G5 

lower scries was indicated as equivalent to the beds which Gilbert 
called Permo-Carboniferous, and attention was again called to the 
equivalence of this general Permian section with that described by 
King in the region to the north. It was further suggested that the 
Permian, as found in the Kanab section, must extend toward the west, 
east, and southeast in Arizona and New Mexico. 

Permian fossils, consisting for the most, part of plant remains, have 
been reported from various parts of Colorado by members of the 
Ilayden Geological Survey. ' but the collections and the systematic 
study of the formations were not sufficiently complete to establish the 
presence of roeks of this age in such development that they could be 
separated from the Trias above or from the Carboniferous below. It 
thus remained for the present investigation to reveal the occurrence of 
strata with Permian affinities as a definitely separable formation within 
the limits of Colorado. 

The fossils obtained from the Rico formation have been studied by 
G. H. Girty, who reports that the fauna is a mixed one, containing 
fossils of both Permian and Carboniferous affinities. For this reason 
he considers the Rico beds as transitional, and is inclined to retain the 
term Permo-Carboniferous to apply to them. He states, however, 
that if it were necessary to assign the fauna to either the Coal Measures 
or the Permian, the line between the two should be drawn at the base 
of the Rico formation rather than at its top. 

In attempting to establish the position of the Rico beds Mr. Girty 
lias especially considered the section occurring in eastern Kansas 
which has been described by Prof. C. S. Prosser, and finds a similarity 
in the fossils of the Rico formation and the lower part of Prosser's 
Permian, the Neosho and Chase formations, which correspond to the 
Permo-Carboniferous of earlier writers. 

The lower Permian of the Kanab region, described by Walcott, is 
also transitional between the Coal Measures and the typical Permian, 
as shown by a similar mixture of fossils, so that there is good basis for 
correlating the Rico formation both with the Lower Permian or Permo- 
Carboniferous of the Mississippi and with that of the Plateau region. 

The occurrence of typical Permian both in Kansas and in Arizona 
suggests a query as to its presence or absence in the San Juan region of 
Colorado. Upon this point it can only be said that the lower strata 
included in the Dolores formation rest with apparent conformity upon 
the Rico beds, suggesting that the true Permian should be represented; 
but these lower beds of the Dolores have not yielded fossils in all this 
region. Possibly if the Rico formation had been recognized at the 
time the Dolores formation was defined it would have seemed as appro- 
priate to have placed the lower, unfossiliferous portion in the Permian 

'See Report on the geolog ol the Grand River division, by A.C, Peale: U. S. Geol. and Geog. surv. 
Terr, for is::,, p. 71. 

21 CEOL, PT v 2 5 



66 



GEOLOGY OF THE EICO MOUNTAINS, COLORADO. 



as to have included it in the Juratrias; but the latter procedure was in 
accord with the general lithological similarity throughout the Red 
beds, and this correlation can not be assailed by evidence 
The following forms have been identified from the Rico formation: 

Fossils from Iht Rico formation. 



Fusilina cylindrica.* 
Chonetes inesolobus.* 
Chonetes glaber. 
Productus prattenianus.* 
Produotus nebraskensis. * 
Seminula subtilita.* 
Monopteria polita. 
Monopteria polita var. ricoensis. 
Monopteria gibbosa.? 
Posidoniella pertenuis. 
Posidoniella recurva.? 
Aviculopecten occidentalis.* 
Pseudomonotis hawni.* 
Pseudomonotia hawni var. equistriata. 
Pseudomonotis tenuistriata. 
Myalina perattenuata.? 
Myalina subquadrata.* 
Myalina hindana 
Aviculopinna peracuta.* 
Schizodus pandatua.? 

[es marked by .-in asteris! 



Schizodus cuneatus.? 
Schizodus meekanus. 
Pleurophorus subcostatus. 
Allorisma terminate.* 
Sedgwickia topekensis.? 
Edmondia gibbosa. 
Astartella '.' gurleyi. 
Bulimorpha chrysalis. 
Naticopsis altonensis. 
Naticopsis monilifera.* 
Strophostylua remex. 
Euconispira cf. turbiniformis. 
Euconiepira taggarti.? 
Murchisonia '.''.' marcouiana. 

Loxonema '.' | riense. 

Loxonema plicatum. 
Bellerophon giganteus.? 
Bellerophon crassus. 
Pattelostum bellum.* 
Euphemus carbonarius.* 
ur also iii the Hermosa formation. 



Introductory. — All the Juratrias formations of the San Juan region 
are represented in the Rico Mountains. Beginning at the base, they 
are the Dolores Red beds, L,600 feet in thickness: the La Plata sand- 
stone, 250 feet or more, and the McElmo shales and sandstones, exposed 
to a thickness of 300 feet within the area represented on the map, hut 
having a total thickness of nearly 900 feet in the region adjacent. The 
reasons for the subdivision which i- here adopted are fully given in 
the Telluride folio, and there certain moot questions as to age and 
correlation have been fully discussed, 80 that these points need not he 
considered in this place. 

The materials of the lowesl formation are such as might be derived 
from the rapid weathering of a continent made up largely of granitic 
rocks, with areas of schist and quartzite, and are doubtless evidence of 
the former existence of such a land area adjacent to the San Juan 
region at the time of their deposition. The materials arc similar 
and the conditions under which they were laid down were like those 
of the underlying uppermost formation of the Carboniferous, hut 
comparison with the materials of the La Plata indicates a complete 
change of conditions, from such as favored rapid deposition of hetero- 



bpencee.] DOLORES FORMATION. 67 

geneous rock debris to those favoring complete sizing and sorting of 
land-derived materials. Probably the La Plata will be found else- 
where to be unconformable with the Dolores, but in the Rico region 

there is no evidence of any break in deposition. 

The McElnio formation is different from the La Plata in the large 
amount of green clay shale which enters into its composition. Its 
sandstones have the same character as those of the lower formation, 
and no important or far-reaching change of conditions need be postu- 
lated to account for its differences. Though described as Juratrias, it 
seems to be transitional between that system and the Dakota sand- 
stone, of Upper Cretaceous age. 

. These three formations are easily distinguished in the field, and on 
the map the distribution of each is represented by a distinct pattern of 
the Juratrias color. 

DOLORES FORMATION. 

Definition. — The Dolores formation, as described in the Telluride 
folio, has been made to comprise the Triassic strata of southwestern 
Colorado and adjacent territory. The name is derived from the Dolores 
River because of the t} r pical exposures along its course in the Rico 
quadrangle and its known occurrence throughout the greater length of 
the Dolores Valley. Along the upper course of this river and in the 
Animas region the formation has a thickness of approximately 2,000 
feet, but to the west its thickness diminishes until it is scarcely half 
this amount in the vicinity of the La Sal Mountains. The formation 
is composed of generally reddish sandstones, grits, conglomerates 
and shales, and is calcareous throughout. It is delimited below by 
the Rico formation and above by the La Plata sandstone, of assumed 
Jurassic age. Vertebrate, invertebrate, and plant remains have been 
found in the upper part of the formation, and upon their evidence the 
Triassic age of that part of the series is considered as established. 
Whether or not the lower part is correctly included in the Dolores 
remains to be determined by future discoveries. 

General description >m<l sulx/lrlsion. — As pointed out in the Tel- 
luride folio, where it was first described, the Dolores formation has the 
general characteristics of the widely known Red beds of the Rocky 
Mountain region. The strata are mostly of a bright vermilion color, 
but include a gray or green series in the upper half and occasional 
light-colored sandstones and conglomerates in the lower part. The 
rocks comprise sandstones, grits, and conglomerates in alternation 
with sandy shales, with which earthy limestones are frequently associ- 
ated. Throughout the entire thickness the strata are characterized by 
a calcareous cement, in which respect they resemble the rocks of the 
Hermosa and Rico formations, and are in distinct contrast with the 
friable orquartzitic sandstones of the La Plata and higher formations. 



68 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

Individual beds of coarse sandstone or conglomerate of uniform tex- 
ture are seldom more than 25 or .30 feet in thickness, although fine- 
grained and thin-bedded sandstones with only slight textural variations 
may exceed 100 feet. Nearly all beds vary greatly in constitution 
and thickness, so that detailed sections made at points not widely 
separated can seldom be closely correlated. 

The materials of which the Dolores strata are composed were 
derived from granites, schists, and quartzites, which formed a conti- 
nental area in or near the present area of the San Juan during Trias- 
sic time. The coarse grits are made up of fresh granitic sand, and the, 
conglomerates contain pebbles of schist and quartzite, with occasional 
fragments of granite or fine-grained igneous rocks. 

In the Rico region the Dolores may be divided into two parts; a 
lower coarser-grained and unfossiliferous series containing many 
arkose and conglomeratic sandstones, and an upper liner-grained 
series comprising at its base gray and green shales with light-colored 
sandstones and fossiliferous limestone conglomerates and above these 
vermilion-colored calcareous shales and fine-grained sandstones to the 
bottom of the La Plata. 

The total thickness 'if the formation at Rico is approximately L,600 
feet, of which L,100 or more belongs to the lower portion and the rest 
to the upper division. 

Lower, imfossUiferous division. No continuous exposure of the 
lower portion of the Dolores is available for study in the Rico region, 
but from various partial sections its general features are known. The 
character of the strata as -ecu in the lowest beds as exposed in Scotch 
Creek south of the area of our special ma]), in the central portion as 
studied in the southeast corner, and in the upper part as exposed 
within the drainage of Hermosa Creek to the east of the area mapped, 

is shown in the following sections: 

Section [from /"/< downward) •>/" lower portion of Dolores formation in Scotch Creek 
[Base of section only a few feel above the highest fossiltferoua stratum of the Rico formation 

31. Sandstone, micaceous, red or green, carrying a thin layer of coarse conglom- 
erate near the top 10 

30. Arkose sandstone, cross bedded, white 20 

29. Sandstone, micaceous, red and green 6 

28. Arkose sandstone, coarse grained, white 7 

27. Sandstone, i Lpact, micaceous, salmon color to red 10 

26. Calcareous shales, green and brown 5 

25. Sandstone, micaceous and compact, containing layers of gnarly limestone 

from 2 to 12 inches thick 18 

24. Calcareous sandstone, generally red but mottled; contains thin layers of 

gnarly limestone ]5 

2,3. Arkose sandstone, cross bedded and conglomeratic in part; this layer is 
purple at the base and this color alternates with greenish-yellow and red 

bands; in the upper part a. white and cream color prevail 30 

22. Sandstone, rather flaggy, containing a layer of gnarly limestone at the base. 18 



SECTIONS OF DoLOKES FuKMATION. 69 



21. Calcareous Bandstone, shaly in the lower part ami containing gnarly lime- 
stone near the tup; bright red 10 

20. Sandstone, micaceous, massive, becoming flaggy at the top, where it con- 
tains limestone nodules; red 5 

1!>. Calcareous sandstone, containing small limestone nodules near the tun; 

red 5 

is. ( lalcareous sandstone and red arkose, containing limestone pebbles; purple 

ami white in the upper part, red below 12 

17. ( '( >\ ered 12 

16. Arkose sandstone, variegated; red, white, and purple exposed 6 

15. Sandstone, micaceous, flaggy 5 

14. Arkose sandstone, flaggy, becoming finer grained and micaceous in the 

upper part; pink with narrow white bands 15 

13. Arkose sandstone, somewhat conglomeratic in the upper part, and with 
thin shaly bands near the center and at the top; white and pink, irregu- 
lar 1 lands 35 

12. Sandstone, micaceous, flaggy, very thin-bedded at tup; red 10 

11. Calcareous sandstone; a few thin layers of nodular limestone; red 7 

1(1. Sandstone, micaceous, flaggy; red 6 

(« Porphyry, 8 feet.) 
9. Sandstone, micaceous, flaggy, becoming more compact in the upper part. . 15 

8. Arkose sandstone, white, banded with red 7 

7. ( 'alcareous sandstone, rather poorly exposed in the upper part, but flaggy 
and somewhat shaly, becoming more shaly in the lower part, and con- 
taining nodules of limestone; red 35 

li. A rkose sandstone, red above, white below 6 

5. Shale, probably calcareous, contains nodules of limestone; red 5 

4. Sandstone, micaceous; dark purplish red 5 

3. Calcareous sandstone, irregularly nodular and flaggy; contains gray nodules 

of limestone but no well-defined limestone; red 25 

2. Arkose sandstone, micaceous, thin conglomeratic, cross bedded; near the 
base there is a thin black shale which is quite variable; white, with 

bluish and green zones 15 

1. Calcareous sandstone, with a gnarly gray limestone at the top; red 10 

Total _ 390 

The partial sections exhibited at many places in the eastern half of 
the Rico Mountains, as in Whitecap Mountain and the similar porphyry- 
capped summit just east of it, show that the section above given repre- 
sents in a general way the constitution of the entire unfossiliferous 
Dolores, for near the summit of Blackhawk Peak the lowest limestone 
conglomerates appear. 

Section from the base of the Lit J'liiln sandstone doirnirard, ineludiiiij the upper member of 
the Dolores oiid the iiji/iermost .100 feet of the lonrr member. 

[The sectlon'was made on the south slope of the hill seen in PI. I, when- the La Plata sandstone 
appears as a white band, dipping easterly.] 

Feet 
37. From the base of the La Plata sandstone an alternation of calcareous sand- 
stones and shales 200 

86. ( loarse limestone conglomerate, grading upward into a red calcareous sand- 
stone like that which is called " typical Bed beds. " Many of the pebbles 
in these conglomerates have the appearance of being of concretionary 
origin 5 



70 GEOLOGY OF THE RICO MOUNTAINS, COLOEADO. 

Feet. 

35. Finely laminated clay shales of a gray color, with some sandy layers 16 

34. Sandy shale, very thin bedded; red 25 

33. Sandstone, massive and fine grained; dull red 25 

32. Structureless layers; dull red « 15 

31. Limestone conglomerate - 3 

30. Gray shale and line-grained sandstone, alternating, passing downward into 

the next 25 

29. shales < if a gray-green color 11 

28. Fine-grained dull-red sandstone, massive as a whole; rather Saggy in 

detail 30 

27. Limestone conglomerate 10 

26. Gray shales, containing four thin layers of limestone conglomerate... 20 

25. Lin lest one conglomerate 4 

24. ( J ray shales 10 

23. Gray, sandy shales, containing t\v ■ three thin hands of limestone con- 
glomerate; the upper one full of tooth fragments 8 

22. Limestone conglomerate, rather flaggy 3 

21. Sandstone, gray and green 1 

20. Limestone conglomerate 1 

19. Shale and very line-grained sandstones of a gray-green color, containing a 

4-inch layer of limestone conglomerate at the base 6 

IS. Led, structureless shale 3 

17. Peculiar clay shale of a red color, containing plums of red and white lime- 
stone sprinkled throughout; these nodules are from £ inch to 3 inches in 

diameter 10 

hi. Not «ell exposed, bul probably typical led lied- 15 

15. Prominent bed of sandstones, containing blue concretions of limestone in 

the upper part; these concretions show a c centric Structure; orange 

color 11 

14. Typical Red beds, rather shaly 10 

13. Coarse arkose sandstone, conglomeratic in the lower pari 20 

12. Typical Red beds; no! particularly massive 30 

11. Prominent massive beds of the typical Red-bed character; orange color . . 30 

lo. Typical Led beds ami even-grained arkose sandstones :;."> 

!». Typical Red beds ti 

8. Conglomerate, containing pebbles up to 6 inches in diameter 10 

7. Typical Red beds 17 

t;. Arkose sandstone, rather fine grained, massive; dark red :;:> 

5. Typical Red beds 18 

4. Arkose sandstone, cross bedded, white in the upper part, red below 12 

::. Typical Red 1 »eds 2 

•_'. Arkose sandstone, cross bedded, conglomeratic in the lower part 14 

1. Typical Red beds, exposed, aboul 35 

(At this place a fault crosses and the continuity of the section is broken. I 

T"tal ^ 

From these sections it may be seen thai while there are many beds 
of coarse arkose and conglomerate in the Lower division of the Dolores, 
a large portion of the strata ate of the fine-grained calcareous sand- 
stone or sandy shale which is noted as "typical Red beds." In the last 
section given these calcareous marls form fully one-half the thickness 
exposed below the Saurian series, including numbers 1 to 16. 



spencer.] UPPER DIVISION OF THE DOLORES. 71 

The color of the lower Dolores is variable. The arkose sandstones 
and conglomerates are either uniform dull red, red streaked with 
white, or of a pink shade; while the calcareous marls are always bright 
vermilion, and the nodular limestone bands or lenses are usually of 
gray shade. 

No fossils are known to occur in these lower strata, and for this 
reason, and in the light of the occurrence of Permo-Carboniferous 
fossils in the Rico formation, it is thought possible that the coarse- 
grained division may ultimately be found to belong to the true Permian, 
and thus to represent strata which are known in the Plateau region 1 to 
the west and in the Plains region to the east of the Rocky Mountains. 
This is a matter to be settled by future work, and for the present it 
seems best to place the whole series in the Mesozoic. 

Upper , fossiliferous division. — The upper division of the Dolores for- 
mation shows a thickness of 431 feet in the section given on p. 70. At 
Rico it consists of two distinct series. At the bottom there are 230 feet 
of alternating sandstones, sandy and clay shales, and limestone conglom- 
erates. The sandstones are gray or 3^ellow flags, apparently not so 
calcareous as the usual sandstones of the formation, since they are often 
rather friable. The shales are soft and argillaceous as a rule, though 
sometimes sand} 1 -; their color is either greenish gray or a dull red. 
Carbonaceous matter, often representing plant stems, is abundant in 
the shaly sandstones of many localities, but no determinable specimens 
have as }^et been found. 

The coarser limestone conglomerates are made up of rather angular 
pebbles of dense bluish limestone, some of which are 1 or 5 inches in 
diameter, set in a matrix of limestone which is usually earthy and often 
shows an admixture of quartz grains. In some cases, where the peb- 
bles have a rounded form and show septarian cracks, it seems likely 
that they have originated practically in situ, but in the majority of 
cases it seems that they have been derived from the breaking up of 
preexisting limestone strata. If they were derived from the limestones 
of the Hermosa formation it would seem curious that no Carbonifer- 
ous fossil fragments have ever been noted in the conglomerates; and 
their absence allows room for doubting that the conglomerates are 
really made up of broken fragments derived by wave action from out- 
crops of an older formation along the shore adjacent to which they 
were deposited. If the materials were so derived it is further anoma- 
lous that there is so small a proportion of siliceous sand mixed with the 
limestone pebbles, and that limestone strata should have been alter- 
nately exposed and hidden for the formation of the successive conglom- 
erate layers and the strata of entirely different character with which 
they are interbedded. The finer-grained conglomerates are ordinarily 

iTbe Permian ami other Paleozoic groups oi the Kanab Valley, Arizona, by C D. Walcott: Am. 
Jour. Serf., 8d series, Vol X x. 1880, pp. 221-226. 



72 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

but a few inches in thickness in this region. They are almost pisolitic 
in appearance but no concentric structure lias been noted. In the light 
of these difficulties it mar seem possible that the conglomerates were 
derived from the breaking up of limestones in process of synchronous 
formation. This must, however, be regarded merely as a suggestion, 
since the conglomerate has not yet received the study which must pre- 
cede any theory to account for its formation. For the limestone con- 
glomerates the term " Saurian " conglomerates has been used in the 
field, and this was found a convenient designation in the description of 
them in the Telluride folio. The origin of this name is found in the 
fossil bones and teeth of dinosaurs, associated with those of crocodiles, 
which occur generally in the conglomerates*, and which, while usually 
fragmentary in this region, are elsewhere much better preserved. 
They are considered by paleontologists characteristic of the Trias. 

Above the Saurian conglomerate series the remainder of the upper 
division of the Dolores in the Rico region is made up of typical Red 
bed marls and sandy shales in alternation, without coarse sandstones. 
The uppermost strata are of a bright vermilion color. 

In the section given on page To the upper division of the Dolores is 
represented by numbers 17 to 37, all but the last belonging to the 
Saurian series. 

The upper part of the Dolores has been referred to as fossiliferous, 

and so it is in almost every locality where the Saurian series is found 
to outcrop. Fragments of Saurian hones and teeth are by far the 
remains of most frequent occurrence, and though these have proved 
sufficient for identification in some few cases, they are not as a rule 
determinative. A single specimen of a gasteropod, which in the opin- 
ion of T. W. Stanton is a species of Vvviparis, was discovered in the 
Saurian series near Rico. A single Species of fossil plant is known 
from the Dolores formation, which was collected from a coarse con- 
glomerate outcropping upon the river bank north of Rico. This was 
determined as PachyphyUum munsteri by David White. A complete 
discussion of the age relations of the Dolores formation has been 
given in the Telluride folio, to which the reader is referred. 

Distribution <nid occum nee. — The Dolores formation forms the rock 
surface over perhaps half the extent of the area under discussion, 
occurring around the central uplift outside of the Rico beds, and 
extending to the limits of the area mapped, except in the northwest 
and southwest corners, where it is covered by the La Plata sandstone. 
The characters of the lower coarse portion may be best studied at the 
localities of the recorded sections, arid in general in the eastern part 
of the region. Good exposures may be found on the western slopes 
of Whitecap Mountain and of Dolores Mountain, and elsewhere near 
the headwaters of Deadwood and Allvn gulches. In the lower part 
of Silver Creek, while the strata are well exposed above the cliffs 



bpbncek.] DISTBIBUTIOM OF TILE DOLOBES, 73 

of the Rico beds, both formations have been decolorized by the slight 
metamorphism which they have undergone. In Telescope .Mountain 
and in the ridge north from it the coarse scries is well exhibited as to 
its general characteristics, and again in the upper part of Sand-tone 

Mountain and the slopes north of Morse Gulch. As a rule the coarse 
series is not well shown in the western half of the mountains, and 
except in the (dill's south of Burnett Creek is exposed only locally and 
to no great thickness. In the cliffs mentioned several hundred feet of 
these beds are exposed above the Rico formation, but no peculiarities 
are presented. 

In the northeastern corner of the mapped area the Upper Dolores is 
found upon the ridge between McJunkin and Barlow creeks, where 
the limestone conglomerates of the Saurian series are coarser than 
usual and contain, in the case of the lowest beds, some fragments of 
granite and gneiss. In this region the conglomerates carry many 
worn fragments of bone. 

On the west side of the river the Saurian beds outcrop in the ridge 
between Elliott Peak and Sandstone Mountain, above the saddle, at 
11,000 feet, and may be found also on the opposite side of Papoose 
Basin at 11,750 feet, and again upon the main divide west of Sockrider 
Peak. From the structure indicated on the map, considered in rela- 
tion to these outcrops, it is thus seen that all of the Dolores formation 
exposed in the southwestern corner of the area mapped belongs to 
the upper division. 

Southward from Johnny Bull Hill, where the base of the La Plata 
is found dipping toward the north, no horizons are to be recognized 
until the Saurian conglomerates appear through the reversed struc- 
ture on the southern side of the dome at the head of Burnett Creek. 
In the upper part of the southernmost drain of Stoner Creek the 
Saurian series is well exposed and may be studied to good advantage; 
also portions of the series may be examined in the rounded knob 
upon the main ridge to the east, the summit of which is 11,900 feet. 
From this place the base of the upper division falls rapidly into the 
drainage of Wildcat Creek and soon passes beyond the limits of 
the area mapped. 

The only place where rocks belonging to the upper division are 
found in the high eastern mountains is in Blackhawk Peak, where 150 
or 200 feet of the flaggy sandstones of the Saurian series and several 
of the limestone conglomerates are exposed. Elsewhere the higher 
portions of the formation have been completely eroded. 

I.\ PLATA FORMATION. 

Definition. — The La Plata formation has received its name from the 
La Plata Mountain-, where it is characteristically exposed. In the 
Rico quadrangle, as has been pointed out for the Telluride region, it 



74 GEOLOGY OF THE KICO MOUNTAINS, COLORADO. 

is proper to call the formation the La Plata sandstone. It includes 
two massive sandstone strata, with a series of shaly sandstones 
between them, lying- above the Dolores Red beds and below the green 
marly shales of the McElmo formation. 

Description.— The La Plata sandstone is made up of three members. 
Its thickness varies from loo to 500 feet in the San Juan region, while 
toward the northwest, in the Canyon and Plateau regions, it expands to 
two or three times the maximum figure for the San Juan. In the 
Rico region its minimum is not Less than 250 feet, while its greatest 
thickness i- nearly 500 feet. 

The basal member of the La Plata is ordinarily about 90 feet thick 
in the Rico region, though on the west fork of the Dolores it dimin- 
ishes to 10 feet at one place. It is a tine-grained saccharoidal sand- 
stone, very massive except for a few feel at the top and bottom, and 
cross bedded on a large scale. The direction of the cross bedding is 
extremely variable and seems to he entirely lawless, being verj dif- 
ferent in the part- of the sandstone lying above one another, and 
changing from place to place horizontally. The upper limit of this 
member is frequently revealed by a marked bench or shoulder along 
the slopes upon which it outcrops. The next member is in general 
quite as variable in thickness and i- less homogeneous than the two 
sandstones between which it lie-; within the Rico area it varies from 
7;, to :.'<;•• feet. In the Telluride and Annua- regions its l»a-.' i- char- 
acterized by a dark bituminous lime-tone, but this i- not present in 
the Rico occurrences, though it- horizon i- marked by a calcareous 
sand-tone, probably representing a transition to limestone, in the first 
appearance of the formation east ••(' Rico, A-ide from this stratum 
of local occurrence the middle member i- made up of friable sand- 
stones and sandy -hale- of subdued red tone-, with intercalated layers 
of white sandstones, also friable. The red portions of the -lies 
sometimes resemble the Dolores formation, hut can seldom he con- 
fu-ed with its strata. A thin hand of white sandstone i- frequently 
observable which contains little rosettes of carnelian; a feature which, 
where it occur-, may he safeh taken a- characteristic ><( this middle 
member. In the Rico region the upper sandstone i- uniformly about 
~:> feet thick, being thus thinner than the usual development of the 
lower member, which it resembles both in it- material- and in it- tex- 
ture, and al-o in the cross bedding which it exhibits. 

The materials of the La Plata formation wen- doubtless derived 
from the same continent, and therefore from the same rocks, a- those 
of the sediment- which preceded, hut they were certainly subjected to 
a different and moresevere treatment upon the beaches of the sea. 
Tins conclusion i- suggested by their being very perfect!} assorted 
and composed almost entirely of quartz, in which point they are in 
marked contrast with the undecomposed tirkose, which varies greatly 



si'kncek] LA PLATA FORMATION. 75 

in size of grain and which is so abundant in the Carboniferous and 
Triassic formations. It seems probable that the Jurassic period was 
ushered in b} r a temporary uplift of the San Juan and adjacent land 
areas preceding later sinking which was concomitant with deposition; 
but whatever the physical change may have been which brought about 
these differences of sedimentation, conditions similar to those of Tri- 
assic time have not since occurred in the San Juan region. 

The La Plata formation was studied in the cliff exposure of the hill 
seen in PL I, to the east of the eastern line of this special map, within 
the Engineer Mountain quadrangle. The section is continuous with 
the one of the Dolores formation taken at the same place (pp. 69-70). 
It illustrates the threefold nature of the formation, two massive sand- 
stones being separated by a series of sandy shales and thin beds of 
sandstone. 

Section {from top downward) of the La. Plata formation. 

Feet. 
<>. Sandstone, rusty brown or gray, in banks separated by thin layers of 

crumbling, sandy shale; a few of the lower sandstone layers are calcareous. 73 

5. Red sandy shale 8 

4. White saccharoidal sandstone 4 

3. Sandy shales, crumbling very readily, containing a few thin layers (if sand- 
stone; these are the most abundant in the upper part; about 15 feet from 
the base there is reddish chert in considerable abundance; at 40 feet from 
the base there is a very impure, dull red, earthy and sandy limestone; 

the color of the whole series is reddish 60 

2. Dark, calcareous sandstone, containing considerable calcite near the middle, 

3 to 4 feet 4 

1. Massive sandstone of the usual La Plata character 104 

Total 253 

Distribution and occurrence. — -The La Plata sandstone does not now 
occupy extensive areas in the Rico Mountains, being exposed, as a 
rule, in the upper part of the slopes which border the courses of the 
main streams, where its massive layers are indicated by steeper slopes 
than those in which the Dolores and McElmo formations outcrop. 
Those outcrops which are nearest the center of the dome are at 
approximately the same elevation, and the relations of this formation 
serve very well to show the quaquaversal structure of the Rico Moun- 
tains. This feature is not completely shown on the special map, since 
its extent to the east and north is not sufficient to comprise the adja- 
cent occurrences. Within the area of the special map the La Plata is 
confined to the southwest and northwest corners. In the former the 
La Plata occupies only a small area, but in the latter it is more widely 
distributed, occurring in Johnny Bull Mountain and Elliott Mountain 
and in the drainage which lies between these prominent points. 

The La Plata formation, because of its massiveness, is always promi- 



76 GEOLOGY OF THE KICO MOUNTAINS. COLORADO. 

nent in its outcrop, and especially, as illustrated at Rico, it forms 
knobs where it cuts across the ridges. 

t '/>,■/', hit ion. — The La Plata sandstone represents the lowei portion of 
the Gunnison formation, as described in the Anthracite-Crested Butte 
folio, though exact correlation is not possible, since there appears to 
be no sandstone in the Elk Mountains to correspond with the upper 
member of the formation as known in the San Juan. It is probable, 
however, that the limestone containing fresh-water shells in the Elk 
Mountains represents the same horizon as the limestone which occurs 
in the San Juan, but the latter lias thus far yielded no distinctive fos- 
sils, though sonic indistinct fish scales and vertebra' were found in the 
northern pari of the Engineer Mountain quadrangle. In the Plateau 
region of Utah Dutton recognized a massive white sandstone overlain 
1>\ bright-colored shales and intercalated sandstones, which is distributed 
over a wide area, and this he called the Jurassic while sandstone. 

There is little doubt that it is to be correlated with that portion of the 
Jurassic which has been called the La Plata formation in the San .hum 
region. 

m'ki.mo pobmation. 

Definition. — The name "McElmo" was proposed in the Telluride 

folio for the series of shales and sandstones which lies between the La 
Plata and the Dakota format ions. This formation, like most of the 

others occurring in the southwestern part of Colorado, is quite variable 
in thickness, its minimum being about WO feet and its maximum about 
L,000 feet. 
Description and occurrence.- In the Rico region the McElmo has a 

fairly uniform thickness of somewhat less than 500 feet, and with this 
decrease in thickness it is found to be composed more largely of shales 
than in the Telluride quadrangle, where its thickness is nearly twice as 
great, and where sandstone forms an important (dement of the series. 
These variations in thickness do not interfere, howei er, w ith the certain 
and easy recognition of the formation by reason of its characteristic 
lithological features. It consists of .alternating shale and sandstone in 
variable proportions; the shales are usually apple-green, but some- 
times deep Indian red. with occasional variegated bands of red and 
green. They are tine grained or sandy and occur in homogeneous bands, 
usually several feet in thickness, and within these bands there is little 
or no lamination. The finer-grained strata have a porcelaneous texture 
and a conchoidal fracture, causing the -hale to break up into small more 
or less cubical fragments. The sandstones are usually even grained 
and friable, those in the lower portion resembling the sandstones of 
the La Plata, while at least one of the upper beds is like the Dakota: 
both are white or yellowish and are found to grade horizontally into 
sandv shale, and thence into clav shale. 



spencer.] m'elmo formation. 77 

Perhaps the most constant element of the section is the sandstone or 
conglomerate which occurs in the upper part. This bed is indis- 
tinguishable from the lowest conglomerate of the Dakota, and is char- 
acterized by small subangular pebbles of some white material, which 
is probably impure chert. 

Within the Rico quadrangle. the formation is seldom well exposed, 
though its thickness may be made out in nearly every place, and it is 
found to vary but little. It forms a gentle slope between the steeper 
slopes of the Dakota and La Plata formations. The only section 
which was measured in the Rico quadrangle was found upon the north 
side of the West Dolores, above Love's ranch. At this place there 
was. immediately below the sandstones of the Dakota, 35 feet of fine- 
grained green shale with a few bands of sandstone; next a conglom- 
erate carrying white impure chert about 15 feet in thickness, and then 
an alternation of dull-red and green shales with thin sandstones for a 
thickness of 275 feet, the whole thickness of the formation being in 
the neighborhood of 425 feet. The entire thickness of the McElmo 
does not occur within the Rico special area. As indicated on the map, 
there are five small patches of the formation, distinct from one another, 
lying above the La Plata sandstone. These are tongues which extend 
up along the ridges from the more extensive areas adjacent. 

Correlation. — The McElmo formation represents the upper part of 
the Gunnison formation, as it is shown in the Elk Mountains, and is 
therefore, in part at least, equivalent to the Morrison formation occur- 
ring upon the east side of the Front Range. It has a very consider- 
able but unknown extent in the portions of Utah, Arizona, and New 
Mexico adjacent to this part of Colorado. 

No fossils are known in the San Juan region, but their established 
relation with the Morrison beds must at present be sufficient evidence 
of their Jurassic age. 

CRETACEOUS. 

Although the Mesozoic formations above the McElmo are not pres- 
ent in the area represented by the special map of the Rico Mountains, 
the Dakota sandstone and the Mancos shales occur in the immediate 
vicinity, and the latter is found to pass upward into the coal-bearing 
formations in the Mesa Verde region to the south and in the Lone 
Mesa to the west, and the general geological history of the region 
indicates that all of the Cretaceous formations of the region were laid 
down over the present site of Rico. Judging from the nearest known 
outcrops of these formations, their aggregate thickness was approxi- 
mately 6,000 feet, as compared with 11,500 feet of Mesozoic and Pale- 
ozoic strata below them. 



78 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

The series of conformable Cretaceous formations was terminated 
b}' uplift, 1 after which erosion ensued in the region which is now 
occupied by the San Juan Mountains, as is evidenced by the uncon- 
formable relations of the ensuing formations in the Telluride and Sil- 
verton quadrangles and in the adjacent regions to the north and east. 

i Orographic movements in the Rocky Mountains, by S. F. Emmons: Bull. Geol. Sue Am., Vol. I, 
1S90, p. 'JSO et seq. 



CHAPTER III. 
THE IGNEOUS ROCKS AND THEIR OCCURRENCE. 



Bv Whitman ( ':;<>: 



PETROGRAPHY. 

As has been pointed out in the outline of the geology, the igneous 
rocks of the Rico Mountains belong to a few kinds, most of which 
have been previously observed in association. In the systematic 
descriptions to be given they will be considered under the following 
divisions: Monzonite; porphyries associated with the monzonite; 
hornblendic monzonite-porphyry; porphyry of Calico Peak and 
vicinity; basic dike rocks. 

MONZONITE. 

General description. — The mass of the large stock west of Rico is a 
granular rock containing orthoelase and plagioclase in about equal 
amounts, carrying a little quartz in most places, and with a variable 
development of augite, hornblende, and biotite. The feldspathic 
constituents strongty predominate over the ferromagnesian silicates. 
The rock thus belongs in the group intermediate between the syenites 
and diorites to which Brogger has recently given the name monzonite, 
from the type locality of Monzoni, near Predazzo, in Tyrol. 1 

The rock is, as a rule, of medium grain, the variation in this re- 
spect ranging from rather coarse to fine grain, but not to a texture 
that is strictly aphanitic. With a hand lens nearly all the mineral 
particles can sometimes be recognized in the coarser specimens, includ- 
ing apatite, titanite, and magnetite. The structure is ordinarily 

1 \V. ('. Brogger, Die Eruptivgesteine des Kristianiagebietes. II. Die Eruptionsfolge der triadischen 
Eruptivgesteine bei Predazzo in Siidtyrol, 1895, pp. G-64. The proposition of Professor Brogger to 
establish a group of rocks between syenite and diorite and coordinate in importance with them has 
been so welcome to the petrographers of the United States Geological Survey that the use of the 
terms monzonite and quartz-monzonite in the folios of the Survey has been authorized by the 
Director, in accordance with the recommendation of a special committee. The further proposition 
made by Brogger to subdivide the quart z-monzonites, which stand intermediate betfl een the gran- 
ites and the quartz-diorites, into banatitennd adamellite, according to the amount of quartz pre- 
sent, lias not yet been specially considered. 

79 



80 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

typically granular, with local tendency to a poikilitic development in 
which orthoclase is the host and includes all other constituents. This 
structure is rarely very prominent megascopically, hut almost invaria- 
bly appears in some degree under the microscope. 

In mineralogical constitution the feldspars always exceed the fer- 
romagnesian minerals and the rocks are therefore grayish in color. 
The darker modifications are also the finer grained and often owe 
their shade to the liner particle- of the dark silicates. The two feld- 
spars arc distinguishable in some places through the pinkish color of 
the orthoclase. but this is entirely lacking in man; areas and the rock 
has then the appearance of a diorite, the term which would have been 
applied to these masses a few years ago. 

The lime-soda feldspar, plagioclase, has the usual development in 
such rocks, being in rude crystals about which the orthoclase has 
oriented itself to some extent, as seen in some of the thin sections 
examined. A combination of the albitic and Carlsbad twinning laws 
is not rare, and applying the Michel Levy method to such crystals it 
has been found that labradorite of Ab x An, is the most common plagio- 
clase. There i> strong zonal structure in many crystals, and it is 
possible that andesine is also present in individual crystals in some 
places. 

The unstriated feldspar is undoubtedly orthoclase. It occurs in 
anhedral grains, often idled with dusty inclusions giving it the pink 
color above mentioned. Without tendency to form regular crystals 
it almost invariably surrounds grains of other constituents and often 
presents the poikilitic structure in line development. No microper- 
thitic intergrowth wa- observed. 

Quartz is present only as a very subordinate constituent in small 
angular grains intimately associated with the orthoclase. In some 
portions of the mass it constitutes several per cent of the rock, which 
then becomes quartz-monzonite, or banatite, if the term proposed by 
Brogger for such types he accepted. As a whole, the amount of 
quartz may be considered as accessory and not requiring recognition 
in the name. 

The granular rocks of the stock are characterized in contrast to the 
monzonite-porphyiy of the prevalent sheets by the appearance of 
augite and biotite as dark constituents. Ln some of the most distinctly 
granular forms of certain knolls on Darling Ridge the only dark sili- 
cates present are augite and biotite, but in other places hornblende 
appears in abundance, often intergrown with augite. It is developed 
to the exclusion of augite in rare instances. This hornblende, though 
dark green in color, is more vivid in hue than that of the porphyry 
sheets and has a somewhat weaker pleochroism. 

Apatite and titanite are prominent accessory constituents of these 
monzonites. The latter is distinctly visible in the hand specimen in 



cboss.] MONZONITE. • 81 

honey-yellow crystals of the common development. Apatite occurs 
in a few Large crystals, and not infrequently the naked eye may detect, 
the glassy hexagonal prisms with pyramid. Magnetite is quantita- 
tively of less importance than usual, and its development is like that 
of apatite, viz, in a few Large grains easily detected with the unaided 
eye. 

Variations qfth-e monzonite. The variations in texture and in com- 
position above noted bear no evident causal relation to the boundaries 
of the stock as now exposed. Now hornblende, now augite predomi- 
nates all through the mass. The finer-grained rocks are not necessarily 
near the borders, nor are the facies richest in dark silicates so related. 
No abrupt boundaries between modifications were seen, such as might 
indicate that certain forms were later intrusions. It is true that the 
exposures are not sufficiently continuous to warrant the assertion that 
there are no dikes cutting the main mass. Indeed, it seems probable 
that there are dikes of the porphyry, to be described in the next sec- 
tion, but none of granular rock was observed. It appears, therefore. 
that the magma filling the stock conduit was nearly homogeneous and 
suffered no considerable differentiation in situ. 

JSdations />> :>ther occurrences. — No chemical analyses of the Rico 
monzonite have been made, as it seemed unnecessary in view of those 
already existing of nearly related rocks collected by the writer from 
other stocks of southwestern Colorado. In the table below are given 
analyses of four monzonites of this region and of two foreign rocks 
from classic localities. 

21 geol, rx 2 ti 



82 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

Analyst'* nf intmzrmilt' and quatiz-tiimizmiilf. 



( nnstituent. 


<■ 


»■ 


in. 


IV. 


V. VI. 


SiO, 

AU>, 

IV.,< ».. 


65. 70 
L5.31 
2.54 


65. 84 

15.23 
3. 93 


63.91 

17.07 
4. 39 
1.51 

.81 
4.47 


57. 42 
18.48 

3. 74 

2.10 

1.71 
o. 84 

4. 52 
.".. 71 

.OS 


57. (ill 
17.23 
7.28 

2.20 
5. 32 


55. 53 
16.80 
4. 06 
3. 35 
3. 00 

0.00 


FeO 


1.62 i 

1 . 62 2. 21 

2. 56 4. 74 


MgO 

CaO 


NajO - 

K,0 

H. 2 below 110° 

H 2 above 110° 


3. 62 

4. 62 

■1 


2.96 3.48 
3. 02 3. 7-1 


3.41 4.31 
4.01 :',57 


. 98 . 33 


. 28 . 70 


.09 
.09 


Tin 


.33 

. 03 

Trace. 

. L2 

.03 

Trace. 




.so 




95 


PjA 




21 


. 36 




47 












03 

.09 
.15 




Mn< • 




' .It! 

.13 


I'.al l 








Lid 


:::::::::::::::: 




Trace. 


FeS 






.04 








Total 


99.53 - .- 99.92 100.45 ' 100.17 

















I. Quartz-monzonite (banatite). Northeast of San Miguel Peak, Telluride quad- 
rangle, Colorado, Telluride folio, X... 57. Geol. Atlas of D. 8., 1899, p. 6. Analyst, 
II. N.Stokes. 

II. Banatite, Szaszka, Banat. Quoted by W. ('. Brdgger, Die Eruptionsfolge der 
triadischen Eruptivgesteine bei Predazzo in Siidtyrol, 1895, p. 62, Ajialyst, Th. 
Scheerer. 

III. Quartz-monzonite (banatite). Sultan Mi tain, near Silverton, Colorado. 

Analyst. L. G. Eakins. 

IV. Augitic monzonite. Babcock Peak, La Plata Mountains, Colorado. Analyst, 

H. X. Stokes. 

\'. Monzonite. Monte Mulatto, Tyrol. Quoted by W. C. Brdgger, loc. cit., |>. 62. 
Analyst, Lemberg. 

VI. Monzonite. LaPlata Valley, aboveBasin Creek, La Plata Mountains, Colorado. 

Analyst. W. F. Ilillebrand. 

The position of the Rico monzonite is near the two rocks from the 
La Platas. If these analyses be compared with others discussed h\ 
BrOgger in the publication from which two partial analyses have been 
quoted it is still more plain that the rocks in question are typical 
members of the groups to which Brflgger has given the names mon- 
zonite and quartz-monzonite or banatite. 



crow.] POBPHYEIE8. 83 

PORPHYKTES ASSOCIATED WITH THE MONZONITE. 

A group of porphyries of obscure occurrence has been observed in 
the landslide area of Darling- Ridge. None of them is represented on 
the map because they were seen only in dislocated blocks, and none 
could be traced sufficiently to establish its relations to the stock. The 
area in which the rocks in question were particularly noted is to the 
east nf the South Fork of Horse Gulch and in the main gulch a little 
below the forks. In this vicinity there arc in the more or less broken- 
up blocks many small exposures of porphyries characterized b}>- green 
augite, by feldspars exhibiting a microperthitic intergrowth both in 
phenocrysts and in groundmass particles, and in some cases by con- 
siderable quartz. As an extreme form may be cited the rock pene- 
trated by several tunnels on the south side of Horse Creek not far 
below the south fork. In these rocks there is sometimes but little 
plagioelase, and certain ones can only be called syenite-porphyries. 
At a small ledge outcrop the rock is almost granular, with but little 
augite. and biotite and no hornblende. 

These alkali-rich rocks do not extend out of the landslide area, 
except possibly in the basin of the South Fork of Horse Gulch, where 
they are concealed by talus and wash. Much of the material of "The 
Blowout" is of these rocks intimately associated with monzonite, but' 
in the crushed and greatly stained condition of all the rock in this 
vicinity no clear idea was obtained as to the relative importance of the 
two types. It is considered probable that the monzonite stock rock 
is cut by the alkali-rich porphyries. 

HOKNBLENDIC MONZONITE-PORPHYRY. 

General description. — The intrusive sheets and dikes occurring in 
the Rico Mountains are nearly all of one chemical and mineralogical 
type, but present many minor structural variations, which were no 
doubt caused by slight local differences in the conditions attending 
their consolidation. The structural modifications do not obscure the 
similarity in composition when the rocks are studied under the micro- 
scope, but some masses are too fine grained for the unaided eye to 
recognize their constitution with certainty, and decomposition often 
renders the character obscure. 

The rock of the larger sheets and of many dikes is a very distinct 
porphyry of general light-gray tone with an even balance between 
phenocrysts and groundmass. The most abundant phenocryst is a 
plagioelase, determined in some eases to be labradorite (Ab, AnJ, 
developed in the common stout prismatic crystals. Dark green horn- 
blende in small prisms is the only other constant and essential pheno- 
cryst. Small quartz crystals, almost, invariably well rounded by 
resorption, are sparingly present in a few cases, but can usually be 



84 GEOLOGY OF THE RICO MOUNTAINS, COLORADO 

detected in the hand .specimen only on close scrutiny with a lens. The 
gray and homogeneous-appearing groundmasa consists of orthoclase 
and quartz. 

The most striking variation in structure noticeable in these rocks 
arises from the development of the plagioclase phenocrysts. These 
arc much more abundant than hornblende and, as a rule, are larger. 
But they may be nearly uniform in size or present a gradation from 
the largest to those scarcely distinguishable by the naked eye. In the 
Montelores sheet, for example, the plagioclase crystals are uniformly 
of 2 to 3 mm. diameter wherever that mass was examined. More 
commonly there are numerous crystals of 5 mm. or more, though sel- 
dom reaching a size of 1 em. in diameter. The common color of the 
plagioclase is white, and the centers of the larger ones may be clear 
and glassy. In many places the crystals have become clouded by 
ferritie particles and muscovite. 

Tlie e position of the plagioclase crystals in the Hico porphyries is 

imt ~o easily determined as in many similar rocks. Carlsbad twins 
are rare, hence the Michel Levy method of identification is inappli- 
cable. But the extinction in the zone normal to the albitic lamellae 
reaches 20 in many instances noted, from which it may be inferred 
that labradorite (Ab, An,) LS abundant. As the same variety was 
found common in similar porphyries of the La Plata Mountains it is 
believed that labradorite is the common phenocrysl in the Rico mon- 
zonite-porphyries. 

The hornblende of these porphyries is always of the common green 
variety. In many masses it is developed only in distinct prisms, 
which are. however, always -mailer than the plagioclase and subordi- 
nate in amount, hut in several cases a considerable pari of the horn- 
blende is in so small prisms that it either obscures the groundmass or 
at least gives a d ar k | ()M e t,, the rock. None of the hornblende 

belong-, to the groundmass period of consolidation, a- may he clearly 
seen under the microscope. 

The accessory constituents of these porphyries— magnetite, apatite. 
titanite, and allanite— occur in small phenocrysts, often distinguish- 
able to the naked eye. Magnetite alone occurs usually in two gener- 
ations, the earlier and larger grains being occasionally included in 
plagioclase and the fine dust of the later period being disseminated 
evenly through the groundmass. Magnetite is the most abundant of 
these accessories, but yet is quantitatively of little importance. Apa- 
tite and titanite play the roles usual in such rocks. Allanite, appears 
in single small prisms in several thin sections and is probably spar- 
ingly present in all the masses. 

No augite or biotite has been observed in any of these porphyries. 
They are hornblendic rocks, and differ thus very constantly from the 
dike porphyries associated with the monzonite stock and from the 



PORPHYRIES. 85 

soda-rich, quartz-free mOnzonite-porphyry occurring- in a large dike 
crossing- Bear Creek and the Dolores River near the mouth of the 
former. 

The groundmass of this homblendic monzonite-porphyry consists 
chiefly of orthoclase with a subordinate amount of quartz. Plagio- 
clase enters into its constitution in only two or three observed cases, 
and in those instances quartz was not determinable. The structure is 
often evenly tine grained, the component minerals occurring in sepa- 
rate particles. In the coai\ser developments of this structure quartz 
may show a tendency to regular form. The presence of quartz is 
made distinct in many rocks by the cloudiness of the orthoclase grains, 
contrasting with the clearness of the quartz. 

Not infrequently the grains of the groundmass are comparatively 
large, but the two minerals are intergrown in complex and apparently 
irregular manner, producing a patchy modification of the micropoiki- 
litic structure. This is generally evident only between crossed nicols, 
and, if there are quartz phenocrysts present, aureoles of oriented 
quartz filled with dusty orthoclase are always found about them. The 
groundmass grain often varies without regard to the visible size of 
the porphyry bodies; still, the narrower dikes and thinner sheets are 
commonly of very fine grain. An uneven development of the ground- 
mass particles is found in numerous cases. 

Decomposition products. — Decomposition of these porpl^-ries greatly 
obscures the constitution to the unaided eye, but seldom prevents clear 
recognition of their characters under the microscope. Hornblende is 
frequently entirely decomposed and replaced by a mixture of chlorite, 
calcite, quartz, and ferritic hj'drates in varying proportions. The 
chlorite gives the rock a dull-green hue and obscures its composition 
when deposited secondarily in particles throughout the groundmass. 

The feldspars are always more or less clouded in the common man- 
ner, and this may add to the distinctness of the porphyritic structure 
if the orthoclase in the groundmass is chiefly affected. It then is usu- 
ally dull pinkish and causes the white labraclorite phenocrysts to stand 
out in increased prominence. On the other hand, if both feldspars are 
equally affected the phenocrysts become scarcely distinguishable from 
the groundmass. Calcite is common in small amount. Epidote may 
develop either from hornblende or in the mass of plaglioclase crystals, 
as has often been described. 

Relationships of t his porph yry. —The predominant porphyry of the 
Rico Mountains, above described, is practically identical with many of 
the rocks occurring in the Henry, Carriso, El Late, and La Plata 
mountains and in many places in Colorado. In a description of these 
pocks by the writer, 1 published some years ago. they were called 

1 The laccolitio mountain groups of Colorado, Utah, and Arizona: Fourteenth Ann. Kept. U.S. Geol. 
Survey, 1894, pp. 167-241. 



86 



GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 



"hornblende-porphyrite" in the scMi.se of diorite-porphyry. the more 
prominent development of the plagioclase being considered as sufficient 
ground for assigning the rock to the diorite family. But with the 
establishment of the monzonite family it, is (dear that a large number 
of the rocks of the Henry Mountains and other laccolithic groups are 
porphyrinic members of that intermediate family. The same type of 
porphyry occurs in many places in Montana and has been described 
under various names — by [ddingS from the Yellowstone Park. 1 and l>y 
Pirsson from the Little Belt 8 and Judith 8 mountains. 

In the table below is given a list of analyses of porphyries very 
similar to the Rico mon/onitc-porphy rv so far as t lie feldspars are con- 
cerned, though showing some variation in the amount of quartz and in 
the dark silicates, biotite and sometimes augite accompanying tilt' 
hornblende. 

Analyses of quartz-bearing monzonite- and diorite-porphyries. 
st, W. i - HUlebrand.] 



SiO 

\l.o, 



Fefi - '. 

FeO 

MgO 

CaO 

NajO 

KjO 

H 2 belcra 11" 
HjO above L10' 

CO, 

TiO, 

PA 

MnO 

Ba() 

SrO 

Li,( ) 



I>inr i i e-porphyry, 

Deadu 1 Gulch 

La Plata Maun 

tains. 



60. ii 
16.67 
2.31 
3.09 

2. is 

1. 22 
5. 18 

2. 71 

I. 13 

. is 

60 

. 29 
. 13 
. [2 
. 11 
Trace. 



M on /. i« n i i e-po 
phyry, Reve 
Crag, Mount ni 
I era, n e n c 
Mountains 



Monzonite- 
porphyry, 

3iei raCarrisi 



62.88 

17. 13 
1.86 
2. 58 

1. is 
:.. 39 
1.50 

2. 25 
. L6 
.42 



ii'.l.di 



.7.1 

.26 
. [6 
. 16 
. 12 
Trace. 



63. is 
16. 17 
2. 36 
2. 28 
1.33 
4.77 
I. in 



. 17. 

. 15 

.09 

Trace. 



99.86 



i Geology of the YellowstoneNational Park: Hon I ,Vol.XXXII,Pt.II,1899,pp.9<l 97. 

- Petrography of the igneous rocks of the Little Belt Mountains, Montana, by L. V. Pirsson : Twen- 
tieth Ann. Rept. C. S. Gcol. Survey, Pt. Ill, 1900, p. 518. 

3 Geology and mineral resources of the Judith Mountains of Montana, by w. I [.Weed and I.. V. Pirs- 
son: Eighteenth Ann. Rept. U.S. Geol. Survey, Pt. in. 1898 p 



cross.] BASIC DIKE ROCKS. 87 

1'ORPHYRY OF CALICO BEAK AND VICINITY. 

A rock of unusual character was found occurring in dikes in the 
vicinity of Calico Peak and probably forming- an important part, 
if not the whole, of the alunitized cone of that mountain itself. It 
has been given a special color on the map. This rock is a porphyry of 
most marked appearance, characterized by large orthoclase pheno- 
crysts in considerable abundance, some of them exceeding an inch in 
length. Associated with these prominent crystals are many smaller 
ones of plagioclase and augite, biotite, or hornblende. Quartz crystals 
are rare. The groundmass of these porphyries is quite different from 
that of the common sheet rock. It has much plagioclase and little or 
no quartz. On the whole it is estimated that the rock is much nearer 
the stock monzonite in composition than would be inferred at first 
sight. In the development of green augite and brown biotite there is 
a further link connecting this peculiar type with the monzonite. 
None was sufficiently fresh for analysis, but it is probable that the 
rock is somewhat richer in alkali feldspar than the monzonite, and 
hence approaches a quartz-bearing syenite-porphyry. 

In point of time these dikes cut the earlier and common monzonite- 
porphyry, but have not been observed in contact with the granular 
stock rock nor with the basic dikes soon to be described. The rock 
of Calico Peak has not been found in sufficiently fresh condition to 
allow of its certain reference to this type, but it is plain in many 
places that it bore large feldspar crystals, and it is also known that 
dikes of the rock in question in Bull Gulch have undergone alteration 
like that of the Calico Peak rock and in such cases resemble the 
latter very closely 

BASIC DIKE ROCKS. 

The geological map represents a number of basic dike rocks occur- 
ring sparingly in various parts of the Rico Mountains, and a few others 
were observed in small exposures. These dikes are seldom more than 
a few feet in width and their length is apparently not great, though 
none of them has been accurately traced to its end. They are often 
irregular in course and are effectually concealed by slight coverings 
of debris, for they do not often form projecting ribs. The most 
prominent of these basic dikes is that shown on the eastern border of 
the area. This has been traced to the northeast over the crest of the 
divide between Barlow Creek and the Silver Creek drainage, and it 
exceeds 20 feet in width in some places. 

Rocks similar to these occur in the La Plata Mountains, in the 
Durango, Engineer Mountain, and Telluride quadrangles, and, in fact, 
all over the country adjacent to the San Juan Mountains, as far as 
it has been carefully explored. There is much more variety among 



88 GEOLOGY OF THE EICO MOUNTAINS, COLORADO. 

these dikes than is represented at Rico, where one type prevails to an 
unusual degree. In spite of the variations these rocks are apparently 
connected in origin with the intrusive sheets and stocks of monzonitic 
magmas described above. They cut all other rocks and are distinctly 
the latest igneous masses of the region. 

From their constant association with monzonite- and diorite-porphy- 
ries in southwestern Colorado these rocks might be assumed to be 
melanocratic diaschistic dikes, according to the genetic classification of 
Broo-o-er, but it must be confessed thai the complementary leucocratic 
magmas required by such an assumption did not come to eruption in 
the Rico Mountains. From the great variety of these basic dike rocks 
in southwestern Colorado it would appear that nearly all the known 
kinds of lamprophyres or melanocratic dike rocks may be present. 

The basic dike locks of the Rico Mountains are closely related as 
far as can now be ascertained, but few are fresh enough to allow an 
accurate determination of their normal composition. The ferromag- 
nesian silicates greatly predominate, common greenish augite being 
the most constant and abundant, with variable amounts of olivine, 
reddish-brown biotite.and brown cainptonitic hornblende. Magnetite 
is present rather sparingly. The feldspathic constituents are partly 
orthociase, partly plagioclase, and analcite may have been present in 
some cases, being now largely replaced by secondary products. The 
habit of the freshest rocks is deeidedh basaltic, through the abundance 
and form of development of augite and olivine. 

From the comparatively subordinate r61e ordinarily played by pla- 
gioclase, these rocks fall in the group named by Rosenbusch olivine- 
bearing augite-vogt sit* . 

PHENOMENA OF INTRUSION. 
PORPH1 1:1 MASSES. 

Centers of eruption. It is clear from an inspection of the geological 
map that while the porphyry sheets have a general concentric distri- 
bution about the center of uplift, they are specially numerous in the 
two groups of peaks into which the Kico Mountains are divided by 
the Dolores Valley. There are but very few sheets present in the 
valley itself at the stratigraphic horizons in which they are most 
abundant on either side. The Montelores sheet is a notable exception 
to this rule. 

On the west side of the dome the porphyry masses are most 
numerous in the semicircle of peaks from Expectation Mountain around 
to Soekrider Peak. The gi-eatesl number of observed irregularities 
in the sheets, such as crosscutting and forking, is also to be found in 
these summits. It therefore seems plaily indicated that the principal 
source of these masses is the complex of (likes situated in the center 



cross.] CENTERS OF ERUPTION. 89 

of this semicircle at the forks of Horse Gulch, but unfortunately the 

exposures of this interesting locality are very restricted. 

In the canyons of the three forks of Horse Gulch porphyry forms 
rugged cliffs seeming at first to belong to a large mass, but in the 
north fork in particular a close scrutiny reveals the fact that there is 
a very complicated interlacing of dikes, of which the drawing of the 
map is but a poor generalization. The sedimentary rocks are found 
in strips or angular blocks between dikes, and form but a small part 
of the exposures. Since all the rocks of this vicinity have been 
thoroughly impregnated with pyrite and stained by its decomposition 
products, it is necessary to examine the cliff faces foot by foot to 
recognize the form and extent of the porphyry masses. In g'eneral 
the dikes of the north fork have a prevalent north-south ti*end, with 
many intersections. 

To the south these dikes pass under the alluvium of the valley 
bottom, and in their strike, in the gorge of the south fork, is a mass 
of porphyry apparently much more continuous than that above 
described. But the exposures are here more limited, and beyond the 
actual borders of the gorge the outlines of the porphyry are effectually 
concealed, as shown b} r the map. 

In the middle or west fork of Horse Gulch a large series of dikes is 
revealed in the walls of the little canyon. These trend nearly east 
and disappear under the soil and forest growth, which comes to the 
brink of the gorge. It is probable that these dikes are offshoots from 
the mass of the south fork, a relation indicated by the poor outcrops 
of sandstone alternating with prophyry at the mouth of the latter on 
the west side. The drawing of the map is much generalized in the 
representation of all these dikes, for not only are they obscure, but 
there is such a network that a much larger scale is necessaiy for their 
accurate delineation. 

In spite of the poor exposures, it is plain that at the forks of Horse 
Creek is the most notable eruptive center of the porphyry magmas to 
l>e found in the Rico Mountains, and by its relation to the sheets of 
the adjacent peaks it seems likely that here is the principal channel 
through which the magmas of the latter ascended to the horizons of 
lateral intrusion. On the east side of the north fork the connection 
between two sheets and the dikes was found to be well exposed, and 
on that basis the other sheets found to approach closelv to the dikes 
of the canyon are also represented as offshoots. 

The various dikes and sheets of this center belong for the most part 
to the common type of hornblendic monzonite-porphyry, varying only 
in grain, but on the North Fork of Horse Creek a somewhat darker 
type of finer grain was observed to cut the prevalent varietj^ in dikes 
and to send off thin sheets on both sides. This facies is actually but 
little different in composition from the principal form. 



90 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

On the east side, of the Dolores the porphyry sheets are most abun- 
dant in the vicinity of Blackhawk Peak, but no center of eruption at 
all corresponding to that of Horse Gulch has been found. It is possi- 
ble that the porphyry mass of the lower part of Allyn Gulch is a 
crosscutting body, but no evidence to that effect was obtained, and it 
seems more probably a part <>f the Newman Hill sheet. 

The magma of the sheets in the eastern pari of (lie Rico dome may 
possibly have come up through fissures on the border of the dome. 
In this case they have been deflected to stratigraphic horizons on 
reaching the Dolores formation. In this connection it may be pointed 
out that the largest mass of monzonite-porphyry known in the region 
occurs but a few miles to the northeast, beyond the influence of the 
Rico uplift, in Heiniosa Peak and Flattop. 

Stratigraphic distribution of sheets. The observed sheets of the 
Rico Mountains represented on the map are evidently most numerous 
in the Dolores formation. Instances are not wanting of their occur- 
rence both above and below the Dolores, hut especially for the lower 
horizons the few sheets present in the Rico and 1 lennosa format ions 
only serve to emphasize the preponderance noted. It is rather singu- 
lar that sheets are not more numerous at the soft shale horizons between 
the massive limestones of the Ilermosa. Possible reasons for this dis- 
tribution are given in the next section. 

As to the occurrence of sheets above the Dolores formation, it must 
be confessed that data upon this point are wholly wanting on the east- 
ern side of the river ami that the mass of Elliot! Mountain proves that 
at least some masses did reach above the base of the La Plata sand- 
stone. In the similar group of the La Plata Mountains a great many 
sheets occur in the .Jural rias and also in the ( 'retaceous. although the 
principal horizon of intrusion is there, as here, in the Dolores forma- 
tion. It must be assumed as probable that at least a few sheets were 
intruded into the Cretaceous beds of the Rico dome. 

The relation of the sheets 1o the Rico dome structure is discussed in 
Chapter IV. 

Small dikes. -There are many small dikes and tongues of porphyry 
in the vicinity of the larger Bheets. Many of these are above larger 
masses, and it has been generally assumed that they represent minor 
arms or offshoots, such as must occur in the fissured sedimentaries 
adjacent to the principal masses, rather than the main feeders or chan- 
nels through which the magma- of those larger bodies ascended. It is 
true that neither observation nor theory demands that the conduit sup- 
plying the material for a large intrusion should be of corresponding 
size, and some instances were observed where a narrow dike seemed to 
be the supply channel for a large body. 



CONTACT METAMORPHISM. 91 



MONZOMTE STOCK. 



Form amd dimensions. — Although the actual contacts of the large 
stock of Darling Ridge are revealed in but few places, and much of it 
conies within the landslide area, it is believed that the outlines of the 
mass and its relations to adjacent rocks are correctly understood. The 
northern limit of the stock is in the bed of Horse Creek, a short dis- 
tance below the forks. From this point it extends nearly 2 miles 
southeasterly to the base of the prominent ridge between Sulphur and 
Iron gulches, and its maximum breadth of about three-fourths of a 
mile is between these gulches. 

On the crest of Darling Ridge a tongue of sediments with a por- 
phyry sheet crosses from the southeast onto the Horse Gulch slope 
between two masses of monzonite. It is impossible to make out defi- 
nitely in the confusion of the landslide surface whether the smaller 
body of monzonite is a branch of the main stock or is separated from 
it by the sedimentary arm. In all probability the former is the case, 
and if the contact of the stock were laid bare many other projecting 
arms would no doubt be exposed. 

Relation to porphyry sheets. — The stock was seen to cut off porphyry 
sheets in a few places, but the view that it is distinctly later than all 
the porphyries of the main type is based principally upon the relations 
exhibited in the La Plata Mountains between stocks of a very similar 
monzonite, as well as others of diorite and syenite, to hornblendic 
monzonite-porphyry in intrusive sheets. There the sto r ks cut across 
all sheets in their courses. The diorite-monzonite and other stocks of 
the Telluride quadrangle also cut intrusive porphyries of the same 
general character as the Rico porphyry. 

PHENOMENA CONNECTED WITH IGNEOUS INTRUSION. 

In the introductory chapter it was pointed out that the intrusion of 
molten magmas in the area of the Rico Mountains had been accom- 
panied by phenomena of contact metamorphism about the monzonite 
stock and followed by local solfataric action at Calico Peak. 

Contact metamoiphisni. — The sedimentary rocks adjacent to the 
porphyry sheets and dikes are often somewhat indurated, but seldom 
exhibit pronounced niineralogical changes. About the monzonite 
stock, on the other hand, a high degree of metamorphism has taken 
place; limestones have become marbleized and several silicates of lime, 
magnesia, iron, and alumina have been formed. Of these garnet is 
the most common, while various pyroxenes and amphiboles are also 
abundant. Specular iron is very common accompanying these sili- 
cates, and the magnetite deposit found in the shattered limestones on 
the north side of Darling Ridge may possibly be classified with the 



92 GEOLOGY OF THE BICO MOUNTAINS, COLORADO. 

products of the metamorphic epoch. Almost the entire area of the 
contact zone about the monzonite stock is greatly obscured by land- 
slide and other surface debris. 

The association of contact metamorphism with stocks of granular 
rocks has been observed by the write]- ;it a Dumber of localities in 
Colorado, and the absence or slight amount of such action in the 
vicinity of large laccoliths of porphyritic rocks has been a most strik- 
ing fact. In no case has any considerable development of garnet. 
vesuvianite, pyroxene, or amphibole been noted in the contact /one 
about porphyry intrusives corresponding to the granular stock rocks. 
Since in the La Plata Mountains, as well as at Rico, the porphyries 
and the granular rocks are similar in chemical composition but differ 
in structure and mode of occurrence, the suggestion IS natural that 
there is some genetic relation between the process of metamorphism, 
the development of the granular structure, and the stock form of 
eruption. The further discussion of this relationship will lie reserved 
for a review of the observed occurrence- of stock rocks iii Colorado. 
which it i- the u titer's desire to complete at no distant day. 

Solfataric action. The alteration of the porphyry of Calico Teak 
into a rock consisting largely of alunite. a hvdrous sulphate of alu- 
mina and th<' alkalies, ha- already been referred to in Chapter I. This 
alteration can l»e explained only as the result of the attack of sul- 
phurous agents, and from the circumstances of occurrence there can 
be n<' doubt that the action i- to he attributed to solfataric emanations 
<>)' the Rico eruptive center in the period of waning igneous activity. 

The cone of ( alien Peak i- made up of a light-colored rock w Inch is 
either nearly white or stained various shade- of red and yellow, often 
in brilliant hue-. The rock has either a marked porphyritic structure 
or is highly brecciated. Mo contacts were -ecu. owing to tin' exten- 
sive talus Blopes which conceal it on all -ide-. a- represented in PI. 
Yll. The alteration i- so extreme that it i- not certain that all of the 
rock belongs to a -ingle mass, though it i- apparently of that character. 
The rock of the greater pari of the peak \\a- plainly porphyritic 
ami contained many large feldspar crystals, and from this fact it is 
-upposed that the rock was originally of the type of monzonite 
porphyrj with Large phenocrysts of glassy orthoclase, which has been 
described above and which occurs in fresh form only in the vicinity 
of Calico Peak in long dikes represented on the map. In its presenl 
condition the rock of the peak contains no dark silicate-; the former 
feldspar phenocrysts are represented either by a mass of white kaolin 
or by a granular mass of a nearly colorless mineral, ordinarily too Hue- 
grained for recognition. The groundmass i- grayish in tone and may 
be tine or coarse grained. In some places the rock has become largely 
a porous quartzitic mass. The room of the larger feldspar crystal- i- 
seldom completely tilled by the alteration product, which usually 



cross.] SOLFATARIC ACTION. 93 

appears as an aggregate of rude plates, a definite crystal outline being, 
however, rare. These plates are rough crystals of alunite, the basal 
plane predominating and being bordered by the low hemihedral pyra- 
mid commonly developed in this mineral. No good crystals of polished 
faces were found. 

At several places the freshly fractured rock was found to exhibit a 
very distinct yellow color in the porous areas representing feldspar 
phenocrysts, the color being due to native sulphur in minute round 
crystalline particles. 

The more massive rock found in many places consists of a coarse- 
grained aggregate of irregular rude tablets with kaolin filling the 
interstices. Small veins of uniform fine grain also traverse the rock 
locally, the character of the material being unrecognizable megascop- 
ically. 

The general character of the Calico Peak rock was recognized by 
the writer from its resemblance to the quartz-alunite rock found by 
him in the Rosita Hills, Custer County, Colorado. In the latter case 
the material was formed by solfataric action upon rhyolite in a small 
volcanic center, 1 and the alunite made up a much smaller part of the 
rock than at Calico Peak. But fairly good crystals were found in the 
Rosita Hills, associated with diaspore. 

Microscopical study of the Calico Peak rocks confirms fully the iden- 
tification of the principal substance of the Calico Peak mass as alunite,' 
and shows that kaolin and quartz are the only other minerals of impor- 
tance present in the specimens examined. Diaspore has not been cer- 
tainly identified in these rocks, and the chemical analyses given below 
show that there can be but very little present. 

In the table on the following - page are presented quantitative analyses 
of two of the Calico Peak specimens and one of a rock from the Rosita 
Hills. I is the analysis of a coarse-grained rock almost resembling a 
pearly gray marble from the west slope of Calico Peak. II is a fine- 
grained white vein on the south ridge of the peak. Ill is an alunite- 
quartz rock from Mount Robinson, in the Rosita Hills, republished 
from the descriptions cited above. Analyses I and II are by George 
Steiger and III was made by L. G. Eakins, all in the laboratory of 
the Geological Survey. In the column following each analysis is given 
the molecular ratio. 

1 Geology of Silver Cliff and the Rosita Hills, Colorado, by Whitman Cross: Seventeenth Ann. Rept. 
U. S. Gcol. Survey, rt. II, 18%, pp. 52-56. On alunite and diaspore from the Rosita Hills, Colorado: 
Am. Jour. Sci., 3d series, Vol. XLI, 1891, pp. 466-475. 



94 



GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

Aitali/xt'x < if tlluiiitr rucks. 



Constituent. 


'■ 




11 




III. 


Si0 2 


2. 54 

35. 24 

o42.35 

.08 

4.(12 

::. 27 

. 13 

1 1 . 99 


42 
440 
415 

65 
35 

666 


1.79 

37.92 

a37.66 

.38 

2. 12 

6.77 

.06 

L3.03 


30 
474 
370 

34 
72 

724 


69.67 

it. 27 

13.72 

.07 

.34 

2.44 

J <n 


114 
134 

! « 

263 


so.. . 

\\M, 


\a ,< 1 

K ,o 


II .0 below no° 


11 ,0 above 110° 




Total 


99. 62 




99. 73 




100.24 





... .... no :i.i p 1 > 11 present 

From the molecular ratios of I and II it appears thai the substances 
analyzed consisted mainly of alunite with a little kaolin. The alkalies 
area little below the required amounts for the sulphuric acid found. 
but if the Losses of the analyses be assumed to be soda, and the lime 

be supposed t<> replace alkali in alunite. the analyses are very satisfac- 
tory. It i> notable that the vein alunite (II) is much richer in K,() 
than the replaced rock 1 1 1. 

The alunite-bearing rock of the Rosita Hills contains a great deal of 
quartz, bul the Calico Peat mass is, in some parts at least, nearly pure 
alunite. 



COMPARISON OF THE RICO MOUNTAINS WITH LACCOLITHIC 
CENTERS OF ERUPTION. 



'I'},, laccolithic mountain groups. From the western summit of the 
Rico Mountains the observer has spread out before him a plain coun- 
try, dotted with widely separated groups of peaks, which has become 
celebrated the world over for its examples <>t' the laccolithic type of 
intrusion of igneous magmas into sedimentary rocks. In the far dis- 
tance, and visible only when the atmosphere is especially clear, lie the 
Henry Mountains, which will always be classic ground for the student 
of the laccolith.' Nearer to the point of \ iew are t he Abajo or Blue 
Mountains, the La Sal, El Late and ( 'arri-o groups, and. close at hand, 
the La Plata Mountain-. In all of these groups of mountain- the igne- 
ous rocks arc similar in character as well as in their intrusive forms of 
occurrence, as has been definitely shown by the writer in a review of 
the observations made in the early exploration- of the Powell and 
Harden surveys, with description- of the rock- collected by Gilbert, 



'■'"•■ "f tin- II. 



d.oss] LACCOLITHIO POBPHYBIES. 95 

Holmes, and others. 1 Since that review was published opportunity 
has been afforded the writer to study in detail the La Plata Mountains 
and parts of the San Miguel Mountains and to examine other localities 
in which the laccolithic type of porphyry occurs. Additional material 
representing the rocks of the Henry and Carriso mountains has also 
come into his hands. 

At the time of the review above mentioned all the available rock 
specimens from the Henry, Abajo, El Late, Carriso, and San Miguel 
mountains collected by the earlier geological explorers were of one 
structural type of porphyry, and exhibited no great range in mineral- 
ogical composition. They were described as "porphyrites," mainly 
hornblendic and quartz bearing, but having a considerable amount of 
orthoclase in the groundmass in every case. It is now evident that 
most of these rocks are monzonite-porphyries or orthoclcbse-hearing 
diortte-porphyries.* Additional material from the Henry Mountains, 
collected by Prof. Marcus E. Jones, and from the Carriso Mountains, 
collected by Mr. C. R. Corning, fails to reveal the presence in these 
groups of other types of porphyry than those already known. 

The only granular rock collected from the mountain groups in ques- 
tion, by either Gilbert or Holmes, was by the latter from the La Platas, 
but its mode of occurrence was not distinguished from that of the por- 
phyries. The recent investigation of that group has shown that the 
specimen in question came from a stock of monzonite in the heart 
of the mountains, and that both syenite and diorite are also present 
in stocks. All of these granular rock masses of the La Platas cut 
many intrusive sheets of diorite- or monzonite-porphyry. Thus it 
appears that one of the groups supposed by Holmes to be like the 
Carriso, El Late, and Abajo mountains, and due to injection of por- 
phyry sheets, is in reality more complex in its igneous history. 

The San Miguel Mountains were also classified by Holmes among 
the groups of summits due to great intrusions in Cretaceous shales, 
and the specimens collected by him in Lone Cone and other western 
summits indicate that his idea is true in part. But the detailed sur- 
vey of the Telluride quadrangle revealed that the Mount Wilson or 

'The Laccolith' Mountain Groups of Colorado, Utah, and Arizona, by Whitman Cross: Fourteenth 
Aim. Bept, V. S. Geol. Survey, Pt.II, 1891, pp. 157-211. 

In this article the terminology of Gilbert -was followed in the word laccolite, but since its publica- 
tion the writer has become convinced that the form laccolith is preferable, both from the etymology 
ami to avoid correspondence with the ending of mineral and rock names. 

'The writer approves most heartily of the usage now common in America by which the word por- 
phyry and all of its derivalh es are reserved exclusively for the designation of rock structure. Cer- 
tain of the laccolithic rocks are intermediate between quartz-bearing mouzonite-porphyry and 

quartz-hearing diorite-porphyry. They thus become porphyritic equivalents of granodiorite, as 
recently defined bj Lindgren (Am. Jour. Sci., tth series, Vol. IX, 1900). While the writer believes that 
the rocks to which the name granodiorite is applied by Lindgren must be recognized bj a distinct 
name, that term seems to him objectionable, since the rocks are not in fact intermediate between 
granite and diorite— the conception expressed in the name— but between quartz-monzonite (banatite) 
and tonalite. If granodiorite be finally accepted by petrographers, many of the laccolithic rocks of 

the I treat Plateau region must be Called granodiorite-porphyry. 



96 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

eastern group of the San Miguel Mountains was due to a great stock 
of diorite-monzonite cutting andesitic tuffs of the San Juan series 
and the Eocene (?) San Miguel format ion. and hence that these peaks 
are in fact geologically a part of the San Juan Mountains, cut off by 
erosion. A hasty examination by the writer in 1899 of Dolores Peak, 
lying between Lone Cone and Mount "Wilson, showed the presence 
at that point, also, of tuffs and underlying San Miguel beds, besides 
some porphyry masses and crosscutting bodies of granular rock, from 
which it appears that this mountain is more closely related to the San 
Juan Mountains in origin than to the laccolithic groups, as supposed 
by Holmes. 

Stocks and laccoliths of the Telherid quadrangle.- The Mount Wil- 
son stock does not occur in close association with intrusive porphj lies 
and is but one of a number of large stocks of monzonite, diorite, or 
gabbro, now known to cut the volcanic series of the western San Juan 

Mountains. These stocks are independent of centers of laccolithic 

intrusion or of local uplift of domal character. Hut large laccoliths 
of diorite- or monzonite-porpln r\ do occur in the same general region, 
as in Grayhead, Whipple, and Hawn Mountains, and in Flattop, a 
few miles northeas! of Rico. These laccoliths are all in the ( Jretaceous 
shales and there is no folding oi Faulting of the underlying strata. 

In the case of both the stocks and the laccoliths of the Telluride 

quadrangle there i< no apparent reason, such a- structural weakness 
in the crust, for the eruptions at the points where the masse- are 

found. 

Relations of th Rico Mountains. 'The Rico Mountains are related 
to all the groups of laccolithic mountains mentioned above in that they 
contain a large number of intru>ive sheet- of the common types of 
porphyry occurring at a center of local uplift, with which the intru- 
sion- themselves have had more or less to do. Bui their most inti- 
mate relationship i- to the La Plata Mountain-, the only other center 
in which crosscutting stocks of granular rocks are known to occur. 
The stock rocks are in both cases similar in chemical composition to 
the sheet porphyries, bu1 represent later eruptions of \er\ differenl 
physical conditions. 

But while the Pico Mountains are in some respects much like the 
La Platas in the occurrences of porphyries and granular stock rocks, 
they are unlike any other center of eruption with which they 
have been compared in the variety and extent of the volcanic phe- 
nomena exhibited and in the principal element- of the local structure. 
In Chapter IV will be found a discussion of the Pico dome and of the 
role played by the eruptive rock- in its formation, from which it will 
appear that the structural feature- are not chiefly due to igneous 
intrusion, and that the intrusions may even be regarded as due to the 
earth stresses which have produced the principal structure. This 



cross.] RELATIONS OF THE RICO MOUNTAINS. 97 

conclusion rests upon the insufficiency of the exposed igneous masses 
to produce the structure seen, the improbability of the existence of 
hidden masses of importance, and the abundant evidence of fault 
blocks thrust up in the heart of the dome since the porphyry intrusions. 

The solfataric activity and the later spring action of the Rico center 
may be due to proximity to the great volcanic center of San Juan or 
to the fracturing of the rocks in the period of faulting. Possibly also 
the deeper dissection of the dome by erosion has revealed the 
action of agents which have been, to some extent at least, in opera- 
tion at corresponding depths at other centers. 

From the character of the Rico and La Plata mountains it is evi- 
dent that the La Sal, Abajo, El Late, and Carriso groups must be 
reexamined in some detail before the conclusion that they are genet- 
ically of the simple laccolithic origin ascribed to the Henry Moun- 
tains by Gilbert can be finally accepted. 

21 geol, pt 2 7 



C H A P T E E 1 V. 
STRUCTURE OF THE RICO DOME. 



Bv Whitman Cross and Aki 



INTRODUCTION. 

The stratified rocks of the Rico district have been described in a 
preceding chapter, from the lowest Paleozoic known in the, region to 
the base of the Dakota Cretaceous. In thickness, however, these 
rocks represent only about half of the known section of southwestern 
Colorado, reckoned to the top of the Laramie. The thickness of the 
strata exposed in the vicinity of Rico may be given as approximately 
5,300 feet, as shown in the following table. 

si,-, ,/,, , vposed hi vicinity "( linn. 

Feet 

Daki ita 150 

McElrao 600 

La Plata 250 

Dolores 1, 800 

Rico 300 

Hen,,, isa 1 , 800 

Devonian 400 

Total 5, 300 

The thickness of the higher Mesozoic strata in adjacent regions, as will 
be brought out in the forthcoming folios of the La Plata andDurango 
quadrangles, is approximately l.Tuo feet. If. then, as seems probable, 
all these higher formations originally extended across the site of the 
present San Juan Mountains, the sedimentary section, in the western 
part of the region at least, was no less than 10,000 feet, in thickness. 
There is every reason for supposing that the whole of this thickness 
covered the site of the Rico Mountains at the close of the Mesozoic. 
Continental uplift was succeeded by enormous erosion in the area of 
the San Juan Mountains, but there arc reasons for supposing that 
about 2,000 feet of the Cretaceous beds remained in the vicinity of 
Rico to be covered by Tertiary volcanic rocks, like those still pre- 
served in the adjacent parts of the San Juan Mountains to the east and 
98 



CROSS AND SPENCER.1 SAN JUAN DOME. 99 

north. About that thickness of Cretaceous shales is exhibited under 
the rolcanics in Mount Wilson, only 9 miles directly north of Eico. 

While there are evidences of several important orographic disturb- 
ances in the San Juan region prior to that at the close of the Laramie, 
the most notable structures now visible in the sedimentary beds about 
the mountains are due to that movement. There have been other 
movements since the eruption of the Tertiary volcanics, and one of 
the most interesting- problems which this region presents is connected 
with the recognition of these later periods of deformation and the 
differentiation of their effects. Unfortunately, in the case of the 
Rico dome there are no intrinsic data for determining its age relative 
to the broader structures observed; so far as the facts there presented 
are concerned the quaquaversal fold might have been formed at any 
time since the deposition of the highest rocks involved — the Mancos 
shales. Consequently, all age determinations applied to this feature 
are founded upon the general geological data of the region, and espe- 
cially on facts concerning the age of the igneous rocks. 

THE BROAD SAN JUAN STRUCTURE. 

San Juan dome. — The San Juan Mountains are flanked upon the 
south, west, and north hj sedimentary formations which dip away 
from the central mountainous mass of crystalline and semicrystalline 
rocks. Upon the east the relations are not well known, but so far as 
the evidence goes it indicates that such strata as have escaped erosion 
dip toward the east, or that in their absence the surface of the granite 
upon which they once rested slopes in this direction. 1 The structure 
is thus seen to be that of a broad quaquaversal fold. Its diameter in 
an east-west direction along a line drawn through Rico and the central 
portion of the Needle Mountains and thence to the Piedra River is 
upward of 60 miles, and the amount of arching along this line, esti- 
mated from a restoration of the Dakota sandstone, is approximately 
10,000 fee^t, an amount equal to the thickness of the Paleozoic and 
Mesozoic formations involved. Upon the Rico side this amount of 
depression of the Dakota is reached between the two branches of the 
Dolores, but slight northwestward dips continue for many miles beyond 
this into the gently warped plateau region, which as a physiographic 
province may be separated from that of the San Juan Mountains in a 
somewhat arbitrary maimer on some line of steeper dips. Thus, on 
approaching the mountains from the west it is seen that the surface of 
the Dakota is cut through by deep canj^ons as it rises gently toward the 
center of uplift until, along a general course adjoining the La Plata 
and Rico mountains, the beds begin to rise more steeply under the 
immediate influence of the San Juan dome. The dissected table-lands 

'For the general structure of this region sec tlie Atlas of Colorado, Sheet XV, Hayden Geol. and 
Geog. Surv. Terr., 1877. 



100 GEOLOGY OF THE KICO MOUNTAINS, COLORADO. 

of the west may be considered as a part of the Plateau region, while 
the more diverse topographic foi-ms to the east are naturally placed in 
the mountain province. 

The San Juan uplift must be regarded as a regional expression of 
continental movements which have occurred since the deposition of all 
or nearly all of the Mesozoic. The first great uplift preceded the depo- 
sition of the San Miguel conglomerate; 1 another is witnessed in the 
upturning- of Tertiary beds of Puerco" (Eocene) age south of Durango, 
and this or still another upward movement is indicated by the attitude 
of the San Juan formation upon the north side of the Needle Moun- 
tains in the headwaters of the Rio Grande and in the tilting of water- 
laid beds occurring in the volcanic complex of the Silverton region. 

It is suggested as an hypothesis for future corroboration, but for 
which indications such as above noted are not entirely wanting at 
present, that the doming of the San duan region lias been the result 

of successive deformations in the same direction, repeated at each 

period of continental uplift affecting this and adjacent regions. 

Rico -'/"/ La Plata domes. The structure of both the Rico and the 
La Plata mountain group- i- quaquaversal. Each is a dome which 
locally affects the structure of the broader San Juan dome near its 
periphery. Neither of these smaller domes i< symmetrical, for in 
partaking of the general structure each has added to the dips of the 
larger dome upon the outside and ha- tended to neutralize them upon 
the inside. Thus, in the case of the La Plata dome notable local dips 

are wanting upon the northeast Bide, and in that of the Rico structure 

they are low or absenl upon tl a,-t and southeast; consequently 

both dona- open out toward the central mountain mass of the San 
Juan. 

Relation of load dames to larger structure. — The Rico and La Plata 
secondary domes are probably genetically related to the broader San 
Juan structure, though how close the relationship may have been can 
not now be determined, since the interconnection of igneous intrusion 
and continental ami orogenic uplift of the Rocky Mountain type 
is not yet understood. In both cases the preservation of the moun- 
tain- a- regions of high topographic relief is due to the presence of 
igneous rocks which have been more resistant to erosion than the 
sediments would have been alone. The intrusions are in the ton;, t 
stocks, dikes, and sheets. To the latter, which may in cases have 
sufficient thickness to he of the type known as laccoliths, a certain 
amount of the observed deformation of the stratified rocks is certainly 
due. In the La Plata Mountains the mass of intruded matter of this 
nature shown in the horizons exposed i- comparable to the defor- 
mation they have suffered over and above that affecting the lower 
formations, which are covered and therefore beyond observation, so 

i See Telluride folio. Sayden map, loo. cit. 



cboss and spenceb.] STRUCTURE OF THE RICO DOME. 101 

that if the porphyry included in the hidden strata should bear the 
same proportion to the sedimentary rocks as in the observed section, 
the doming would be accounted for without additional uplift. At Rico 
the structure and make-up of the dome is much better exhibited, and 
though a working hypothesis that the observed structure might be 
due to a huge laccolith lying between the Algonkian and the Paleozoic 
rocks was at one time entertained, it is now known that such a mass 
of igneous rock does not exist, and that the amount of deformation 
which the uppermost strata of the region underwent was several times 
in excess of the amount of igneous material which was intruded into 
the strata below them; that is, the formation of the Rico dome is 
mainly due to a central uplifting force, apart from any actual intrusions 
of liquid rock material. That such a force was also active in the La 
Plata uplift may well be believed, for there, as at Rico, the thickest 
laccoliths or sills occupy a zone, so far as the rocks now remaining are 
able to show, at a distance from the center of the dome, and it is upon 
these peripheral intrusions that the estimate of the sufficiency of the 
porphyries to produce the observed structure was based. 

STRUCTURE OF THE RICO DOME. 

Elements of the structure. — The structure of the Rico dome has been 
well exposed by erosion. Directly through its center the Dolores 
River has cut its course, dividing the mountains into eastern and west- 
ern groups, which are further dissected by the tributaries of the 
master stream. From almost any commanding position within the 
central part of the area the strata may be observed to dip in all direc- 
tions away from the region about the lower valley of Silver Creek, a 
fact which is illustrated in several of the photographs and in the dis- 
tribution of the geological formations as shown on the accompanying 
map. 

Pis. 1II-V1 show the attitude of the strata in accord with the dome 
structure on the slopes of Dolores, Blackhawk, and Sandstone moun- 
tains. The general structure thus exhibited in a large way is found 
to hold also in detail, and, aside from landslide blocks, there are known 
but few instances of strata belonging above the Algonkian in which 
the dip is toward the center. Very locally such dips occur adjacent 
to the several reversed faults of the region, but these are as a rule 
unimportant. 

Were the whole of the deformation expressed by such quaquaversal 
dips the structure of the region would be comparatively simple, but 
this is not the case; the dome is not a simple structure in which the 
strata have been only flexed and tilted; they have also been faulted, 
and in such a manner that the dome effect is increased by the displace- 
ment of the faults. There appears to be no law or order controlling 



102 GEOLOGY OF THE KICO MOUNTAINS, COLORADO. 

the direction of the faults, but to the rule that the upthrow of faults is 
toward the inside of the dome there are only a few exceptions. 

Still another factor in the deformation has been the intrusion of 
porphyry sheets at various horizons. Concerning these it has been 
noted in another place that they arc more abundant in the upper hori- 
zons of the Dolores formation than in any other part of the section, 
so that their effect has been greater upon the higher horizons now 
removed from the central portion of the mountains than upon the 
lower strata which still remain. 

The local structure in those parts of the area wherein it is not 
obscured by surface deposits may be learned from the distribution of 
the formations as 'exhibited on the geological map accompanying this 
report. On this map strike and dip have been indicated by an appro- 
priate sign; the strike by a line drawn in its direction, and the dip by 
a shorter line at right angles to it. indicating the direction toward 
which the strata fall, the am. Mint of deviation from the horizontal 
being indicated in degrees. Aside from this the manner in which the 
formation lines and sheets cross the contours upon the mountain slopes 
indicates clearly the genera] dip of the rocks. Upon the east side of 
the area the structure is well brought out by the lines bounding the 

Rico and the upper part of the Ilerniosa formation, together with the 
accompanying igneous sheets. Upon the wesl side these horizons are 
largely hidden, bul the distribution of the porphyries shows the struc- 
ture, as do also the tongues of the La Plata and McElmo formations 
upon the main ridges. 

ProJUt sections. On PL VIII are presented two profile sections 
through the heart of the Rico Mountains, exhibiting the dome struc- 
ture. These sections are constructed on the Bcale L: 62,500, or about 
1 inch to the mile the scale of the Rico and Engineer Mountain atlas 
sheets and the vertical equals the horizontal scale. 

Section AA extends from the gently inclined flat-topped ridge west 
of Eagle Peak, which lies directly west of Calico Peak, in a direction 
S. 7'.» E., passing through the saddle near the summit of Anchor Moun- 
tain, across the east ridge of Expectation Mountain, through the sum- 
mit of Dolores Mountain, and across tin- Hat ridge south of Blackhawk 
Peak. It shows the extent t<> which the Juratrias and ( iretaceous for- 
mations of Eagle Peak take part in the structure, and the dome is 
specially brought out by the hand representing the Rico formation. 
The flat position of the formations in the 1 tolores Valley is due to the 
strike being so nearly parallel to the course of the section. This sec- 
tion is located to avoid the larger faults and thus to bring out the 
amount of domal folding the more clearly. 

The porphyry sheets of Anchor and Expectation mountains are rep- 
resented as branches of one body to express the fad shown on the 
north face of the former summit. It may be that they arc; distinct on 
the line of the profile. 



U. S. GEOLOGICAL SURVEY 




SECT 




SECT 



CRETACEOUS 





Jl RATRIAS 






LE( 
CARBO 




La Plata 


Dolores 


x /■ 


Rico 




M°Elmo 



PROFILE SECTIONS TH 





.EGf N D 

EHOL'S DEVONIAN 



ALGONKIAN 



IGNEOUS ROCKS 



Monzonite-porphyry Monzoxrite 



Til 



OUGH THE HICO DOMK 



cross and spencer.] DEFORMATION BY FOLDING. 103 

An arm of the monzonite stock is shown as cutting across the strata 
on the eastern slope of Expectation Mountain for the reason that a tun- 
nel nearly on the line of section encounters that rock on penetrating 
the landslide debris of the shoulder projecting into Sulphur Gulch. 

Section BB crosses the Dolores River within the town of Rico with 
a course N. 78° E. On the west it crosses the summit between Storm 
Peak and Landslip Mountain and ends on the sloping mesa of the 
Dakota sandstone between Stoner and Priest gulches. To the east it 
crosses Allyn Gulch and the Blackhawk fault a little above the Maggie 
Mine, and its eastern end is slightly be} r ond the unnamed point seen in 
PI. I where the La Plata, McElmo, and Dakota formations appear still 
possessing the dip of the Rico uplift. 

In Section BB the appearance of the Dakota on either extreme brings 
out the lateral extent of the domal structure, and the gradual change 
to the Plateau country on the west is exhibited. 

The porphyry sheets of the Silver Creek region are represented as 
ascending on the east side of the dome, in harmony with the idea 
brought out in a preceding chapter that the source of the porphyry 
magmas on this side of the dome appears to be independent of the 
center of uplift and situated near its border. 

Amount of deformation by folding. — Deformation has been simply 
defined by Gilbert 1 as "the process by which level strata are trans- 
formed into dipping strata." The result of deformation by folding 
at Rico has been an essentially domal structure, recognizable by the 
attitude and distribution of the geological formations. In so far as 
these are exhibited upon the surface the}- may also serve as a partial 
basis for measuring the amount of deformation which has taken place, 
and by restoring higher horizons, using the known thicknesses given 
at the beginning of this chapter, a fair estimate may be obtained of 
the total amount of the local uplift. 

The. profile sections of PI. VIII give a basis upon which the amount 
of the uplift can be approximately realized at a glance, but a more 
definite conception may be gained by restoring some particular stratum 
to the position it may be assumed to have occupied before erosion of 
the uplifted rocks. 

The most comprehensive view of the Rico structure is to be obtained 
from a consideration of the La Plata sandstone. Before the dome was 
dissected the base of this formation over the summit was at least 4,400 
feet above the lowest rocks now exposed at Rico on the line of Section 
BB of PI. VIII, and probably somewhat higher, since the above figure 
is estimated from the thickness of the Hermosa, Rico, and Dolores 
formations and the Newman Hill porphyry sheet, and takes no account 
of other probable intrusive sheets. The base of the La Plata on this 
estimate must have been at about the altitude of 13,200 feet — 500 feet 

i Geologic Atlas U. s., folio 36,Pueblo, Colorado, 1897, p. I. 



104 GEOLOGY OF THE KICO MOUNTAINS, COLORADO. 

or more above the highest peak of the Rico district. It is plain that 
some of this elevation may be due to faulting, but it will be seen from 
the map that the uplift by dislocation is mainly north of the line of 
Section BB. 

The amount of local doming which is thus indicated may be seen by 
comparing the position of the La Plata in the vicinity. About 5 miles 
north of Rico the base of the formation crosses the Dolores River at 
an elevation of 9,300 feet, showing a fall from the restored position 
over Rico of 3,900 feet, or nearly 800 feet per mile, independent of 
the influence of the porphyry sheet. Beyond this outcrop the north- 
ward dips are continued for only a short distance, so that here we have 
the full measure of the local deformation in this direction. In other 
directions the fall per mile is less, but the dips are continued for a 
greater distance. Thus from the northwest around to the south the 
average deformation or dip slope varies from 400 to 000 feet per mile, 
for a distance of from 5 to 8 miles, beyond which it gradually lessens as 
the distance from the center increases. The diminished dips continue 
for many miles toward the west into the Plateau region. Toward the 
south they fall at the rate ot about 500 feet per mile, and are met by the 
structure of the La Plata Mountains at a distance of about 7 miles. 
Also to the southeast, though the La Plata is missing, the lower strata 
fall at the rate of 300 feet per mile for about 8 miles, where the local 
structure is completely neutralized by the contrary dips away from 
the Needle .Mountain-. To the east a distance of 4 miles finds the 
base of the La Plata 1,700 feet lower than over the top of the dome 
and dipping to the northeast, in which direction it continues to fall for 
several miles. 

The best basis for estimating the position of the La Plata at Rico 
before the uplift is obtained by noting its occurrence in nearly hori- 
zontal position at 9,300 feet in the Dolores Valley at the mouth of liar- 
low Creek, 6 miles northeast of Rico, and at 8,500 feet at the mouth 
of Bear Creek, 12 miles southwest of that town. If the fall in this 
distance of 18 miles was equally distributed before the uplift, as seems 
probable, the base of the La Plata at the site of Rico was near the 
horizon now found at 9,030 feet, limiting the porphyry sheet of New- 
man Hill, and the domal uplift to the restored position amounts to 
3,670 feet. 

Uplift cbue to mt7ntswej)orpkyries. — The additional deformation due 
to sheets and laccoliths can not be estimated excepting in a very crude 
way from the bodies which have escaped erosion. In the central part 
of the area the Newman Hill porphyry, the influence of which has 
already been mentioned in the preceding section, has a thickness of 
500 feet, proved by the exposures and the drill hole sunk in the Skep- 
tical shaft. Another important sheet near the top of the Hermosa 
formation has a maximum thickness of 250 feet where it crosses the 



cboss and spehckb.] DEFORMATION BY FAULTING. 105 

river above Montelores, south of the area of the special map, but 

thins out as it rises with the dome, until it finally disappears entirely 
in Deadwood Gulch. Its distribution is such that it can hardly be 
supposed to have been present in the central part of the dome. Other 
porphyries in this formation, so far as they are exhibited in surface 
exposures, are of minor importance and could certainly in no single 
section aggregate more than 200 feet. 

The Dolores formation seems to have been, for some reason, espe- 
cially favorable for receiving- sheets and laecolithic intrusions; and 
these are localized, with respect to the dome, upon the eastern and 
western sides. The portion of the formation in which they occur does 
not contain similar intrusions to the north or to the south, where cut 
by the Dolores Valley. Whether or not there were like intrusions 
over the central part of the dome can not be determined, but it would 
seem more likely that they did not exist from the fact that no central 
cross-cutting bodies of porphyry which could have fed them are 
known; however this may have been, the porphyries which now re- 
main reach locally an aggregate thickness of perhaps 600 or 700 feet, 
and by this amount must have augmented the arching of the La Plata 
and higher formations. 

The horizons above the La Plata doubtless suffered still more defor- 
mation from injected porphyry bodies, but large masses of igneous 
rock are at present to be seen only in the cap of Elliott Mountain and 
in the Flattop laccolith to the northeast, upon the line between the 
Telluride and Engineer Mountain quadrangles. The former is imme- 
diately above the La Plata sandstone, while the latter lies on top of 
the'Dakota and is capped by the shale of the lower Mancos formation. 

The mass of monzonite which cuts through the sedimentary rocks 
upon the west side of the dome has caused a considerable amount of 
metamorphism in the adjacent rocks, but there is no evidence that the 
strata have been turned up around its periphery. Its influence in 
modifying the dome must be compared to that of the block faults near 
Silver Creek, but there is absolutely no basis for measuring it. 

Deformation fay faulting. — In the process of uplift or deformation 
by which the Rico dome was produced the strata were no doubt fissured 
and fractured to a considerable extent. At the present time a great 
many old fissures may be detected. Most of them are filled by vein 
matter, partly ore-bearing, partly barren; and in some cases the evi- 
dence is clear that the veins are lines of faulting. The displacement 
on the faults varies from more than a thousand feet to that which is 
scarcely measurable. 

The supposition that the faults of the Rico Mountains are fractures 
contemporaneous with the domal folding, merely expressing relief 
of great tension by rupture of the rocks instead of further bending, 
seems in itself natural, but is opposed by the considerations connected 



106 GEOLOGY OF THE BICO MOUNTAINS, COLORADO. 

with the intrusion of the igneous rocks. From the generally accepted 
theories in regard to the relations of igneous intrusion of Laccolithic 
character to domal uplift it is necessary to assume that the porphyry 
sheets of Rico are contemporaneous with or later than the principal 
uplift. But these igneous bodies arc cut by all faults observed to 
come in contact with them. No single instance was found of a por- 
phyry dike ascending on a fault fissure. Further, the monzonite stock 
is traversed by many quartz veins, some of them bearing sulphide 
ores. It is therefore necessary to disconnect the fault phenomena of 
this region from the primary domal uplift, although it is of course 
possible, or even probable, thai some unidentifiable portion of the 
folding accompanied the faulting. 

In character the faults vary from clean-cut fissures to zones of sheet- 
ing or brecciation many feet in width. Extreme brecciation is well 
shown in various portions of the Blackhawk fault, in the Calumet, 
Zulu Chief, and several tunnel- near Rico, in the •'great vein" of the 
northern part of ( '. 11. ( '. II ill. and in the boundary zone- of the Algon- 
kian quartzites in Silver Creek. Sheeting is seen in most of these 
localities. 

The distribution of the main faults is shown by the map. The 
greater dislocations are near the center of the dome, hut a large num- 
ber of lesser fracture- occur in the circle of peaks about it. A glance 
at the ma)) will show that there i- no pronounced -v-tematic arrange- 
ment of the faults. In certain localities the principal fissures may 
bave a common trend, with minor zone- intersecting at oblique angles. 
This i- illustrated in the southeast corner of the region, in Silver 
Gulch, in the Dolores Vallej near Burns, aid in Newman Hill. A- a 
rule, the fault- are nearly vertical, hut dip at variably steep angle- in 
some cases. 

The displacement of the faults in relation to the dome structure i- 
subjecl to a simple rule for nearly all of those found at some distance 
from the center. When even approximately parallel to the strike of 
the strata the upthrow i- on the inside, or toward the center, of the 
dome. The only important exception to this rule IS the great fault of 
Tele-cope Mountain, which must lie classed with the block fault- of 
Silver Creek. 

It i- evident that all fault- obeying the above rule have served to 
increase the uplift near the center of the dome. Bui it must he assumed 
that mo-t of them lie out gradually a- they pass upward, and it may 
be questioned whether any of the dislocations of less than 300 feet in 
amount cut through the Mancos shales, assumed to have overlain the 
Dakota sandstone at the time of uplift. The Blackhawk and Nellie 
Bly fault- aie the important one- following this rule, and their ffect 
at the horizon of the La Plata sand-tone must have been still meas- 
urable bv hundred- of feet. But if the lateral extent of these fault- lie 



cross and spencer.] BEDDING FAULTS. 107 

compared with the diameter of the dome, a.s represented in the sec- 
tions of PI. VIII, it will be realized that the modification of the dome 
by dislocations following the rule stated above was not great and was 
confined to the central portion. 

The faults hounding the Algonkian schists and quartzites differ 
from most of the other faults in that the}- limit small blocks pushed 
up in the heart of the dome. So far as the fractures are known they 
are nearly vertical. The amount of upthrust is indeterminable, for no 
remnants of the Paleozoic sediments lie on the Algonkian blocks. 
These old rocks then represent plugs punched up through the strata 
and porphyry sheets without much, if any, visible disturbance of the 
adjoining beds at the horizons seen. These blocks are comparable to 
the monzonite stock in this respect, but from their small size the dis- 
turbance in the dome structure above them must have been much less 
than that above the stock, assuming that the stock magma did not 
reach the surface. These fault blocks may perhaps be regarded as 
quite analogous to the stock eruption, in that both seem to be com- 
paratively recent manifestations of an upward force suddenly exerted, 
producing vertical fissures rather than folding. If the fault blocks 
represented by the Algonkian rocks of existing exposures extended 
upward for some distance with nearly vertical walls their disturbance 
of the dome structure may have reached to the upper shale scries of 
the Cretaceous, but if they wedged out upward the faulting must 
have been resolved into local tilting of adjacent beds. 

The great fault of Telescope Mountain is so undetermined as to its 
course and its relations to various other possible fissures that little 
need be said here as to its effect upon the Rico dome. If a single 
fault, it must have materially modified the symmetry of the dome at 
the horizon of the La Plata sandstone. 



BEDDING FAULTS. 1 

The term "bedding fault"' is here applied to dislocations which follow 
planes of stratification. 2 Dislocations of this kind are to be observed in 
several of the mines of the Rico district, particularly in the mines of 
C. H. C. Hill and those of Newman Hill. In both places they have 
been the locus of ore deposition, and in the latter have afforded a great 
deal of ore, which, if not so abundant as that occurring in the verticals, 
has usually been much richer. The veins and ore deposits of Newman 
Hill have been studied in detail by John B. Farish and T. A. Richard, 

1 The section on Bedding Fault-, is by A. ('.Spencer. Since the report upon the Rico ore deposits 
can not accompany the discussion of the geology, as was intended.it seems desirable to refer some- 
what fully to the geological features of the peculiar ore bodies of Newman Hill, which are intimately 
connected with bedding faults. A full discussion must be deferred.— W. C. 

'-' Upon the subject of bedding faults see descriptions of the silver and contact faults, by J. E. Spurr, 
in Geology of the Aspen Mining District, Colorado: Mon.U. S, Geol. Survey, Vol. XXXI, pp. 82, 143. 



108 GEOLOGY OF THE EICO MOUNTAINS, COLORADO. 

who have at different times superintended the operation of the Enter- 
prise mine, and in the papers which they have written many valuable 
observations and conclusions regarding the geological relations exhib- 
ited by the ores have been recorded. In both of these papers the 
geolooy of the ••contact*' deposits of Newman Hill is discussed at 
length. 1 

The term "contact" is used at Rico in an indefinite and incorrect 
sense, and has also been misapplied by Farish and Richard. In the 
local usage the word is not applied in its legitimate sense to the plane 
of contact between different rock masses, hut rather to any ore-bearing 
horizon or /one even approximately parallel to stratification. In New- 
man Hill it is applied to a brecciated ore-bearing zone which is not 
necessarily between the same formations throughout its course. 

Quotation from Farish, An accurate conception of the bedding 
fault and of the so-called ••contact" can not be better conveyed than 
by quoting from the above-mentioned papers. Mr. Farish says: 

Attention lias been called to a band of limestone that occurs midway in the series 
ef alternating shales and sandstone strata. It is a grayish deposit, varying in thick- 
ness from 18 to 30 inches, and occupies throughout Newman Hill the same strati- 
graphical position with reference to the other beds. From its close relation to the 
ore deposits, this hand is locally known as the " contact limestone." It is inclosed 
between two layers of argillaceous shale, which are. however, quite different in 
appearance. Tin- overlying stratum is a soft, comminuted, drab-colored shale, vary- 
ing in thickness from 6 to 20 feet. This layer forms an impervious shed to the sur- 
face waters circulating about it, thus leaving the mine workings below comparatively 
dry. The underlying bed is a black, finely laminated shale from 7 to \-> Eeet in 
thickness, which rests upon the series of alternating gray sandstones and drab and 
greenish shales. 

Description of tht " contact" oy Richard. -The description by Mr. 

Rickard 8 is more detailed, and is quoted, in part indirectly, as follows: 

The are. .unts which have been given 8 of a " contact limestone," overlays bya 

"drab shale" and underlain bya "finely laminated shale," may describe certain 

sections of this ore-hearing horizon, hut they do not characterize it as a whole, and 
they give a misleading idea of it- real nature. 

In four parts of the Enterprise mine the contact is found respectively in a crystal- 
line lime, overlain by black shale ami underlain by sandstone; in a lime breccia, 
overlain by sandstone ami underlain by a gray limestone; in a mass of crushed 
quartzose lime, covered by black shale and overlying a blocky limestone; and at 
the bas I gypsum having a maximum thickness of 15 feet, with limestone 

below it.* 

The .hi- of the contact can not be said to he eon lined to any particular encasement, 
but one may venture the generalization that it is to be sought for in a layer of crushed 

'On the ore deposits of Newman Hill, near Rico, Colorado, by John K. Farish: Proc. Colorado Sci. Soc, 
Vol. IV, pp. 151-164, 

The Ei i Rico, Colorado, by T. A. Rickard: Trans. Am. Iuet. Min.Eng. for 1896, Vol. XXVI, 

1897,pp.9 6 

2 Loc. cit., ml 9G3-970 and 976. 

'Referring to ] di ription just quoted. 

'In the Rico-Aspen mine the limestone which occurs beneath the gypsum is blocky in its fracture, 
like- that occurring below the contact in the Enterprise workings.— A. C. S. 



CROSS AND spenceh.1 BEDDING FAULTS. 109 

rock which occurs along a certain horizon marked by a thinly bedded series of black 
limestones and shales. The parts of the contact explored during my period of man- 
agement were very frequently characterized by a distinct breccia made up princi- 
pally, hnt not solely, of lime fragments. Pieces of shale and sandstone were 
recognizable as derived from adjacent beds, and fragments of porphyrite were trace- 
able to neighboring intrusions of that rock. The contact above the Jumbo No. 2 1 
frequently consisted of compact pulverulent lime, graduating into I >reccia overhead 
and underlain by blocky lime; that above the Enterprise 1 was often breccia, shading 
off into blocky lime overhead and underlain by black shale, while; the ore of the 
Jumbo No. 3 1 contact was found between a powdery brown lime and a thin bed of 
black shale. The variability of the stratigraphical position of the ore thus empha- 
sized is due to the nonpersistence of individual beds. The pulverulent lime indicates 
crushing, probably connected with an invasion of porphyrite above it. 

The wavy compact texture of the gypsum suggests an origin by a sulphatization 
of lime breccia through the agency of solutions coming from neighboring ore-bearing 
measures. 

The contact zone has been the victim of all disturbances tending to deform the 
rocks. A thickness of closely laminated shales is laid upon blocky limestones and 
sandstones. To the formation of a fracture the latter rocks would offer no particular 
obstacle, because of their homogeneity, but the upward extension of a fracture would 
be impeded, if not stopped, by meeting a series of beds which, on account of their 
laminated structure, are easy to bend, but hard to break. There is nothing fanciful 
in this reasoning. Thus, it seems to me, the structure of the rocks of the horizon 
now known as the "contact" was the immediate cause of the repeated shattering 
which that horizon underwent. It was the factor which stopped the upward exten- 
sion of the vein fractures and produced the consequent limitation to the circulation 
of those mineral solutions which were the immediate agents of ore deposition. Thus 
is explained the concentration of large masses of ore along this zone, because it 
became a dam, checking the circulation in an upward direction. The fractures now 
followed by the pay veins were unable to break through the shales above the con- 
tact, and though the later cross veins were stronger, they too were stopped by the 
elasticity of these closely laminated beds. In each case, therefore, the force of ver- 
tical fracturing was diverted into a horizontal displacement, which soon made the 
zone under the shales a mass of shattered rock, peculiarly adapted to become the 
place of ore deposition. 

( 'nm in < nl wpon the quotations. — These two descriptions hit practically 
in accord, though the first is, as suggested by Mr. Rickard, somewhat 
misleading because incomplete. Both agree in assigning the fractured 
and brecciated zone in which the contact and its ores occur to a defi- 
nite and limited series of strata at a constant horizon. The fact is very 
clearly expressed by Mr. Rickard that differences in the inclosing rock 
are due to the original local variations in the .strata rather than to the 
crosscutting of the fractured zone from one horizon to another. That 
this is the actual state of affairs throughout the mines of Newman Hill 
is corroborated by the observations of the writers. The sections of the 
contact and subjacent beds given in the description of the Hermosa 
formation (pp. 48-59) show the general character of the zone. The 
marly limestone and blocky limestone just below if were recognized as 
lithologicalrv identical wherever the contact was visited, and while other 

> Names of vertical NK. and sw. veins in iin ■ I .inn pi i ■• mine. 



110 GEOLOGY OF THE KICO MOUNTAINS, COLORADO. 

beds might come and go these were more constant. So distinct is the 
marly or pulverulent limestone from any other stratum in the section 
that little hesitation is felt in suggesting that a similar rock which has 
been exposed in the Sambo and Lake View tunnels, upon the hillside 
south of Horse Creek, is representative of the same horizon. How- 
ever this may be. the ••contact*' of Newman Hill is believed to be a 
continuous and individual stratum within the region thus far explored. 
It is hardly exact to consider the nonpersistence of strata above or 
below the contact as changing the stratigraphic position of that hori- 
zon, as Mr. Kickard has done. Stratigraphic identity may be more 
certainly recognized by tracing a given rock layer horizontally, even 
though its character changes from place to place, than by attempting 
to define it by its occurrence between like strata. 

The discussion of the origin of the brecciated zone of Newman Hill 
by -Mr. Kickard can be indorsed in the main. From the relative 
amount of faulting upon the vertical fissures at depth and in the vicin- 
ity of the contact it i- evident that the shales have taken up the 
strain which resulted below in sharp displacement to the measured 
amount of often l'.". feet or more, by Hexing and slipping one layer 
upon another and bj brecciation. The inference is not. however, 
warranted that fissures were nol produced in the overlying strata; if 
fault- may die out upward, they may also increase upward with a 
change of flexibility in the strata, -o that it is entirely probable that 
main of the fissures which are known to lie prominent below the 
contact reappear above, though they may never have been mineralized 
to the same extent. Evidence tending in this direction may be seen 
in the fault- and fissures in the dills back of Newman Hill, where the 
massive limestones are very much broken up. These may have no 
correspondence, break for break, with faults occurring at depths, but 
they are presumably related in origin to the veins of Newman Hill. 
since they have corresponding courses. 

Origin of the bedding faults. -It is possible that the bedding faults 
at Rico had their origin before the period of faulting, at the time 
when the upward doming was initiated, [f the beds were bent upward, 
then- would naturally be slipping of one stratum upon another, and 
bedding faults would result. Such an explanation is given by Spurr, 
as cited above, for brecciated zones and plane- of dislocation along the 
stratification in the Aspen mining region of central Colorado. 

In the case of most of the bedding faults at Rico there is no way of 
ascertaining whether or not this origin is applicable, but in that of the 
••Newman contact' 1 it is certain that, while the primary break may 
have been due to tension arising from the Hexing of the strata by a 
gentle uplift, a greater part of the movement and brecciation has 
resulted from deflection of movement along fissures crossing the 
stratification. 



, F.oss and spencer] ORIGIN OF BEDDING FAULTS. Ill 

The origin of the "contact" zone of Newman Hill by the slipping of 
the beds on each other during uplift, or by the resolution of movement 
across the bedding into movement parallel to it, ma} 7 seem sufficient to 
account for the phenomena observed, and certainly in the several noted 
cases of bedding faults at other horizons no additional explanation is 
required, but certain further suggestions may still be made to account 
in part for the phenomena of Newman Hill. 

A secondary origin is suggested by Mr. Rickard for the gypsum 
which occurs locally above the contact in the mines of Newman Hill, 
but the facts already stated (p. 53) are believed to be sufficient to prove 
that the gypsum was really formed in a sedimentary way as an original 
chemical precipitate. Wherever it occurs it lies immediately above 
the pulverulent limestone of the " contact," or, as stated by Mr. P. S. 
Rider, the present superintendent of the Enterprise mine, the gypsum 
locally occupies the place of the " contact." 

In the light of the soluble nature of rock gypsum and the evidence 
in the Rico-Aspen mine that it has been very much corroded by cir- 
culating waters, and also because of the variable thickness of the 
gypsum bed, it seems possible that the observed relation of the "con- 
tact" and the gypsum may be significant of the origin of the former, 
and connected with the brecciation of the black shales which are found 
above it. It may be suggested that the gypsum originally occurred 
over the whole region where the pulverulent marl, which now makes 
up the "contact," is found, and that the latter is the insoluble residual 
left after the former was removed by the action of percolating waters. 
Because of the irregularities which would result from the characteristic 
corrosion of gypsum, its removal and the consequent sinking of the 
superjacent strata might well result in a brecciation of the beds origi- 
nally resting upon such a stratum of gypsum as is supposed to have 
existed at Rico. The brecciation observed in the mines of Newman 
Hill may well have originated in this way; especially since it is mainly 
confined to the black shales which occur above the supposed residuum 
of the gypsum. The "contact" zone itself is sometimes brecciated 
and sometimes not, but the strata below it, though consisting of flexible 
shales and brittle limestones in alternation, are not known to be brec- 
ciated at any place. In the breccia, fragments of porphyry derived 
from a thin sheet lying above it are frequently mixed with the pieces 
of shale to a distance of several feet below the base of the igneous 
rock, a feature which would naturally occur under the supposed con- 
ditions, but which could also occur if the brecciation were due pri- 
marily to a differential movement in the rocks. The localization of 
the brecciated zone between a certain thin limestone band below the 
"contact" and the supposed massive sandstones or porphyry above 
worM seem anomalous, if the bedding fault is due primarily to the 
deforming forces, since the black shales which occur beneath the 



112 GEOLOGY OF THE EICO MOUNTAINS, COLORADO. 

"contact" * are similar to those above and rest upon a great series of 
massive beds, above which movement would have been as likely to 
have occurred as at the horizon observed. It would seem even more 
natural if there had been a distribution of such a primary movement 
through the whole thickness of the black shale series. Evidence of 
such movement might also be expected to occur at many horizons in 
the section involved. 

In view of these considerations, it is thought that there is a fail- 
degree of probability for the truth of the hypothesis proposed. It 
does not interfere at all with the conclusions of Mr. Richard that the 
dynamic forces have been dissipated by bending and by shearing par- 
allel to the strata, since such a brecciated zone would, if existing pre- 
vious to the deformation, particularly lend itself to further horizontal 
movement; while, if later than the deformation, it would not atl'ect the 
problem one way or the other. 

ORIGIN OF THE DOME. 

From the foregoing discussion it appears that the structure of the 

Rico .Mountains is in many respects similar to that of the La Plata 
Mountains, and in less degree to that of the Henry Mountains and of 
other laccolithic groups of the plateau country. The intrusive por- 
phyries are of the type common in all these groups, and their intru- 
sion may be plausibly assumed as nearly contemporaneous in all 
cases. Hut while the Henry Mountain- are described by Gilbert as 
entirely d\w to the intrusion of the porphyry masses, it is clear that 
in the Rico Mountains the bodies of porphyry, either visible or rea- 
sonably to be hypothecated, can not be assumed to have caused the 
domal uplift as a whole, both cm account of their small mass and on 
account of their posit ion in the dome. Further, tl sistence of pro- 
found faults later than the porphyries >how> the action at this center 
of a powerful vertical upthrust which is not demonstrably connected 
with igneous intrusion. 

The porphyry sheets in the Rico dome must have produced a dis- 
placement of overlying strata equal to their mass, and this was certainly 
an important element in the upper parts of the dome. So far the 
uplift is due to the intrusion of igneous magmas, and the Rico Moun- 
tains area laccolithic group. The greater pari of the uplift which has 
taken place has affected the whole Paleozoic section and the Algon- 
kian rocks upon which they lie. and thus the small Rico dome comes 
to show close relationship with the much broader San Juan uplift. 
As has been stated in an earlier section, the most prominent struc- 
ture in the San Juan region is pre-Tertiary in origin, but there was 
also uplift in Tertiary time, and it is possible that the Rico dona is 

'The sandstones are nowhere exposed, but are stated by Mr. Rickard to lie above the "conl 



ORIGIN OF THE RICO DOME. 113 

synchronous with the later elevation and a result of the same force. 
The same is true of the La Plata Mountains. But until the structural 

history of the San Juan region has been studied in much greater 
detail the relation between the local uplift of the Rico and La Plata 
mountains and the more nearly continental movements of the San Juan 
region can not be thoroughly diseussed. The developments of the 
investigation of the Rico Mountains make it very desirable to reex- 
amine the so-called laccolithic groups of the plateau country, for in no 
case, with the exception of the Henry Mountains, has the previous 
work in those groups been sufficient to demonstrate their character. 
They may be similar to the Rico and La Plata groups, the igneous 
intrusions accounting for but a portion of the total uplift. For the 
La Sal Mountains the probability of such a complex origin has already 
been pointed out. 1 

In discussing the nature of the forces which have produced the 
Rico uplift, it is apparent that there is a close analog}' between the 
two phases of intrusive action and two phases of structural uplift. The 
primary upward pressure at this center was one to which the whole sec- 
tion of Paleozoic and Mesozoic strata accommodated itself by folding, 
stretching, and no doubt by minor Assuring. It would appear to have 
been a gradually exerted pressure, of the kind generally assumed to 
have forced the magmas of laccoliths and analogous sheets between the 
strata of a sedimentary complex. Corresponding to this idea it is found 
that the distinct poi'phyry sheets of the Rico Mountains are the earliest 
intrusions. 

The fault blocks of the heart of the mountains, made up of Algon- 
kian schists and quartzites, have been thrust up through the folded 
strata with little or no evidence of contemporaneous folding of the 
adjoining beds. This is also the relation of the Darling Ridge mon- 
zonite stock, as far as can lie seen, and also of the similar stocks of 
the La Plata, Telluride, and other neighboring quadrangles. Such 
fault blocks and such masses of igneous rocks seem alike due to forces 
suddenly exerted, producing vertical fracture instead of doming. 
With such an analogy before one, there naturally arises the sugges- 
tion that a mass of magma forming a stock in greater depth may have 
followed the upthrust blocks now revealed. Such an hypothesis 
requires the assumption of very direct connection between the pro- 
pelling forces of magmas and those of continental uplift. But what- 
ever ultimate connection there may be between these forces, there is 
good reason to question the theory that structural elevation and the 
igneous intrusions at Rico are but different phases of one dynamic 
force. 

If it be contended that but one great force has been exerted, it is diffi- 
cult to explain why larger amounts of magma were not intruded into the 

i Laccolltic Diountain groups, etc. 
21 GEOL, PT 1' 8 



114 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

strata of the Rico dome, in view of the large igneous masses of prob- 
ably contemporaneous origin occurring near at hand in comparatively 
undisturbed beds. A single mass of porphyry, exceeding in bulk all 
the sheets of the Rico Mountains pul together, occurs just at the north- 
east base of the dome, and similar large bodies occur on the San 
Miguel River in the Telluride quadrangle. The stocks of the Tellu- 
ride quadrangle appear likewise to be distributed without visible rela- 
tion to any structure of the sedimentarj formations. In other words. 
itappears to be the case thai both laccolithic and stock eruptions of this 
region may be independent of centers of structural movements of the 
crust. Intrusions have occurred at points of structural weakness. 
but have also taken pla.e in much greater volume at points variously 
related to such centers. With this brief reference to the problem of 
the origin of the Rico dome, its further discussion is postponed until 
the investigation of the San Juan region and of the mountain groups 
of the plateau country has furnished much needed data. 

DESCRIPTION OF THE FAULTS. 

Sprud GuLchfauM. This fault runs along the northeast hank, not 
far from the creek bed, with a general course about \. 50 W.,and is 
nearly vertical. It is more plainlj seen a little beyond the southern 
boundary of the area mapped, where the Montelores porphyry sheet 
is dislocated. The line of the break can be closelj determined here. 

and the amount of upthrow is estimated at inailv t00 f eel upon the 
northeast. The fault is not accurately determinable in the lower part 
of the gulch, being concealed bj wash or broken-up landslide material 
of an area shown on the map. If the lower porphyry sheet, which is 
known in the creek bed, exists on the northeast of the fault, it was 
not detected and has been omitted from the map. Bince it is very pos- 
sible that it thins out rapidly to the eastward, t Outcrops do not exist 
by which the northwestern extension of this fault may be recognized. 

It is thought that a tunnel at an elevati >f about 8,725 feet on the 

north side of Spruce Gulch and running nearly east intersects this 
fault, but as the workings were caved in at the time of visit no definite 
evidence was obtained. The course of the fault would carry it into 
the landslide area south of Sulphur Gulch and in the direction of 
Expectat ion Mountain. 

Deadwofjd fault. -This fault crosses Dead wood Gulchat about 9,150 
feet, being hidden upon the north side by the debris which covers 
Newman Hill. On the south side of the creek it may be located accu- 
rately and it- displacement estimated from the position on either side 
of it of the limestone strata belonging to the middle pari of the Ilei- 
mosa formation. The faulting of the massive limestones is apparent 
in looking across Deadwood Creek from the edge of Newman Hill. 



cboss and spencer.] DOLORES MOUNTAIN FAULTS. 115 

The dislocation is up on the north, and amounts to approximately 
250 feet in the cliffs south of the gulch, but diminishes toward the 
east. Its course, where it crosses the creek, is between N. 65° W. and 
N. 70° W. Upon its north side the strike of the strata is N. 40° W. 
and the dip 37° SW., while to the south of the break the strike is N. 
70° W. and the dip 4° SW. 

The economic importance of this fault lies in the fact that it 
displaces the ore-bearing horizon of Newman Hill. There is little 
room to doubt that the black shale and the shale breccia which are 
exposed in the Stephanite tunnel at the mouth of Deadwood Gulch 
represent the black shale series of the "contact," and are continuous 
northward to the workings of the Rico-Aspen mine. These black 
shales are found about 100 feet from the mouth of the adit, which had 
penetrated surface gravels to near this point, The strike of the Dead- 
wood fault would carry it across the Stephanite tunnel, but the occur- 
rence of the black shale at the point mentioned indicates that the line 
of the fault must be somewhat farther south than the exposures of 
shale, and that its course is intersected b}>- the tunnel in the gravel 
area. 

If it were desired to reach the horizon of the "contact" immediately 
south of the fault it would be necessary to sink at least 250 feet, and 
to a greater depth as the distance from the faujt increased, because of 
the souther^ dips of the strata. From present evidence there is no 
reason for supposing that the "contact" would be mineralized south 
of the fault, for it is not so enriched in the neighborhood of the fault 
in the Stephanite workings. 

Faults of Dolor< ss Mountain ami r!<'J/i!ty. — In the area between the 
Blackhawk and Deadwood faults, and extending to the corner of the 
area mapped, there are several faults of minor importance. These 
seem to fall into two systems: The faults of the most prominent sys- 
tem have courses between N. 45° W. and N. 60° W. ; those of the 
second system vary between nearly north-south and N. 20° W. The 
main fissures are nearly parallel in their general trend to both the 
Blackhawk and the Deadwood faults. In amount of throw they range 
from a few feet up to about 400 feet, though they are mostly under 
150 feet. The maximum is reached in two compensating faults to be 
found upon the north side of Dolores Mountain. These breaks may 
be assigned one to each of the two systems, and they consequently 
intersect, as represented on the map. Between them a wedge-shaped 
mass has been dropped. The relations of the eastern fault are very 
obscure throughout, and this is also true of the lower part of the 
western break, but the latter is well shown at the head of the ravine, 
where it displaces the thick porphyry mass which forms the cap of 
Dolores Mountain. Upon the south side of the ridge the rocks are 
very poorly exposed, and the amount of the fault is not definitely 



116 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

determinable. The thin sheets of porphyry which are represented on 
the map may not be all that are actually present in this region, and 
those that have been located do not afford a clew as to the amount of 
displacement. To the cast of this fault the main porphyry sheet must 
thin out rapidly southward, as tin- one found at its horizon on the 
southern slopes is less than 50 feet in thickness. 

Certain of the faults in this region are contrary to the rule of 
upthrow on the inside of the dome, but these are unimportant. 

BlackJiawk fault. — The Blackhawk fault i- so called from the mine 
located upon it where it has the maximum displacement. It has been 
traced from the divide between Allyn Gulch and the northern head- 
waters of Scotch Creek, south of Blackhawk Peak, to the ridge above 
Nigger Baby Hill. It seem- to correspond to the vein of the Pie-eon 
mine upon C. H. C. Hill, and is probably also identical with either the 
A. B. G. or the C. V; G. vein at Burns; or. what is more likely, these 
fault fissures represenl a split ting of the Blackhawk fault. Accepting 
this as correct, the fault is known for a distance of more than 4 miles. 
Its general course is about N. 52 \\\. though there are many local 
deviation- from this direction. The throw i- always up upon the 

SOUthwesl side. 

Kareh i- tlie fault well expo-ed at the surface, and the throw being 

extremely variable it is difficult to obtain accurate measurement of 
the displacement. At Burn- the A. B. G. fissure shows a fault of 
about 50 feet, while the amount upon the C. V. (i. could not be esti- 
mated, but cannot be \'i\ large. In the lower part of Uncle Ned 
draw, opposite the Blackhawk mine, the throw i- 85 or 90 feet, as 
measured by the displacement of the Fusulina layer and the base of 

the Rico formation. These are th d\ place- where it was actually 

measured, and in both cases the fault i- upon a -ingle plane. Upon 
C. H. C. lliil it is not exposed at the surface, but under ground is 

found to lie a lirecciated vein, which ha- a width of 50 feet in the Don 

Cameron tunnel. 

From the bed of Silver Creek southward the dislocation of the 
Blackhawk fault i- very greatly increased. As will be explained more 
at length in describing the Nellie Bly and Last Chance faults, it is 
assumed that a large part of the dislocation <>n those fractures ha- been 
taken up by the Blackhawk fault south of the point- of intersection. 
thus accounting for the great variation in throw upon the latter. Un- 
fortunately the area within which the relations of these fault- must 
be determined is entirely covered by surface wash, and the existing 
mine workings were either inaccessible when this investigation wa- 
in progress or are so situated a- to throw little light upon the subject. 

It is supposed that the Nellie Bly fault crosses the Blackhawk very 
near the Argentine shaft, in Silver Creek. At the time of visit this 
shaft was full of water, but from the best obtainable information the 



sdspescer.] BLACKHAWK FAULT*. 117 

exploration from it was entirely upon the Blackhawk vein. Similarly 
the old workings of the Blackhawk mine, while extensive, were prose- 
cuted without appreciation of the fact that the vein represented a fault 
fissure and were directed to exploration of the ore shoots dipping 
away from the main vein, or of the branch veins, such as the Maggie, 
also located on the eastern side. There is thus little or no develop- 
ment west of the Blackhawk vein where the Last Chance fault would 
meet it if continued across the covered area east of Allyn Gulch with 
the strike observed to the westward. 

The maze of workings in the Blackhawk mine have thus far defied 
any simple interpretation of (he structural relations of the ore bodies 
at this point; but it is plain that the shoots of sulphide ores dipping 
steeply away from the main vein represent replacement deposits in 
the massive limestones of the Hermosa, the upper beds of which can 
be seen in the lower cliffs east of the vein, and the magnitude of 
the Blackhawk fault at this point is shown by the altitude at which 
these same limestones meet the fault in their descent from the north 
slopes of Dolores Mountain. As shown by the map, they are cut off 
by the fault on the northeast side of Allyn Gulch at a considerable 
distance from the lower workings of the Blackhawk. As the dips are 
steep to the east of the fault and several minor faults occur between 
these two points, the statement of the amount of faulting of the lime- 
stones can be only a general one. It is between 600 and 800 feet in 
the aggregate, and most of it belongs undoubtedly to the Blackhawk 
fault. 

The dislocation has taken place upon a fissure zone for a part, if not 
the whole, of the distance between the lower Blackhawk workings and 
the west slope of Blackhawk Peak. Whether the two fissures continue 
separate for the entire length mentioned or unite in the upper part of 
Allyn Gulch is not known, for surface debris conceals the vein from a 
point near the Maggie shaft to the cliffs of Blackhawk Peak, and the 
meager evidence of a few prospects is not conclusive. The branching 
of the vein at the north is very clearly shown on the surface, and the 
wedge of rock between fissures is seen to be crushed, traversed by 
many small quartz veins, greatly impregnated by pyrite, and thor- 
oughly decomposed. A small porphyry dike is seen in this area. On 
the trail crossing this fracture at about 10,350 feet the calcareous beds 
have been much metamorphosed, with production of garnet and other 
unidentified silicates, while scales of specular iron are abundant. Such 
metaniorphism is elsewhere in these mountains restricted to the con- 
tact zone of the monzonite stock. 

The Blackhawk fault is nearly vertical in the main, but has some- 
what undulating walls. At the head of Allyn Gulch, where crossed 
by the ravines heading north of Blackhawk Peak, a tunnel on the fault 
vein exhibits a series of fractures between which the rock is crushed 



118 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

and sheeted. Several walls dip northeasterly at angles between 45° 
and 65°, but the fissure zone as a whole is much more Dearly vertical. 
Between the outer fissures in the cliffs toward Blackhawk Peak is a 
porphyry mass, much crushed, which is interpreted as belonging to 
the large sheet seen on either side. 

At the time the Blackhawk fault was being studied it was sup- 
posed that the mineralized fractures which are to be seen in the Alle- 
ghany. Maggie, and Privateer veins were offshoots from the Blackhawk 
fissure, but the presence of the several important nearly east-west 
faults of Silver Creek ha> since been ascertained, so that it seems more 
probable that these veins are the reduced eastward equivalents of the 
profound faults of Silver Creek. In the case of the Nellie Bly fault 
the identity may be considered as well established upon both sides of 
the Blackhawk fissure. Upon the east aide its throw is not more than 
150 feet, while upon the wist it is much greater. 

Nellu Bly fault. — The claim from which the name for this fault has 
been derived is a rel< .cat ion of ground which was taken up under the 
name of Alma Mater, but which was never patented. The fissure is a 
fault which was lirst recogni/ed upon the surface on the -lope above 
the Iron mine on the north side of Silver Creek. At this place the 
strata upon the north belong to the upper part of the Ilennosa forma 
tion and dip geniU into the hill (strike N. 80 E.; dip 10 tothewesl 
of north), while to the south of the break occur the massive limestones 
belonging to the middle part of the Hermosa, with a strike N. 80 c W. 
and dip 30 to the east of north. The course of the break here is N. 
80 W\, but this changes toward the west to N. 85 W., and finally to 
nearh east-west. The outcrop of the fault rises diagonally across 
Nigger Baby Hill and the fissure is cut in the Eureka tunnel at the 
mouth, in the new or upper Nellie Bly tunnel at 20 feel from daylight, 
and in the upper Alma Mater tunnel at a distance of about 7.". feet 
from the entrance. It also passes through the incline of the old < rrand 
View mine on the crest of the hill and may be recognized upon the 
western slope in a tunnel at 9,830 feet. It is this fault which has 
dropped the ore bodies in the Iron mine down upon the north side. 

In the various place- where it was seen the attitude of the fault 
varied from nearly vertical to an inclination of \'< toward the 
north. The amount of displacement back of the Iron mine must be 
at least 250 feet, and the tilting of the block to the south of the break 
causes a rapid increase in displacement toward the west. The amount 
of the throw at the Grand View incline i> estimated at 750 feet. The 
fault is clean cut wherever observed, and examination of the break 
shows so little evidence of crushing that it is difficult to believe that 
the known amount of displacement could have taken place along this 
fissure. The magnitude of the fault i- very plainly shown near the 
Nellie Bly tunnel, outcrops of the massive limestone of the middle 



cross and spencer.] LAST CHANCE FAULT. 119 

portion of the Hcrmosa occurring on the lower side of the fault within 
a few yards of the Fusulina layer at the top of that formation, on the 
upper .side. 

In the lower part of Nigger Baby Hill upon the w.e.st side the Nellie 
Bly fault is completely hidden by surface wash. Its course would 
carry it under the alluvial fan at the mouth of Aztec Gulch and in 
the general direction of the Aztec vein, which crosses the gulch at 
9,400 feet, with a course approximately N. 75° W. There is thus 
strong probability that the Nellie Bly and Aztec veins are identical, 
and that there is profound faulting upon the west side of the river as 
well as upon the east. The amount of mineralization in Aztec Gulch 
is in excess of that observed on Nigger Baby Hill as regards this 
fissure. There is strong probability, also, that some one of the heavy 
quartz veins, having a nearly east-west course, in the north fork of 
Iron Gulch is identical with the Aztec vein. The Zulu Chief tunnel, 
for instance, cuts two brecciated zones, one near its mouth and another 
about 200 feet from its entrance. Both are accompanied by quartz 
veins, and the former may correspond with the Aztec vein. Unfor- 
tunately it is not possible to determine the distribution of rock in 
place in all this region, so that the amount of possible faulting can 
not be estimated. 

Eastward from the ravine back of the Iron mine the fault is obscured 
as far as the Black Hawk fault, but east of that fissure a fault, sup- 
posed to be the extension of the Nellie Bly, appears, and, gradually 
swinging toward the southeast, throws the base of the Rico formation 
down upon the north to the amount of 150 feet. Still continuing east- 
ward, it may be traced up Honduras Draw and across the ridge at its 
head, where it is covered by the talus and slide rock in the adjoining 
basin, and be} T ond that point dies out as a distinct fault. 

Last Chance fault. — The Last Chance fault takes its name from a 
prospect located upon it where it crosses the main trail on the south 
side of Nigger Baby Hill at the elevation of 9,350 feet. This fault, 
like the last, is important, and, having a course from N. 80° W. to N. 
85° W., is nearly parallel to it. The distance between the two is 
from 700 to 900 feet in the region where both have been located. 
The apex of the fault runs diagonally athwart the southern slope of 
Nigger Baby Hill, rising toward* the west. Its last appearance before 
passing under the surface wash is in the Amazon workings at 9,100 
feet, on the Nigger Baby trail. Still farther west, however, near the 
base of the hill, there are three well-marked fissures in the same 
general course, and about 100 feet apart. These seem to represent a 
forking of the Last Chance fault. 

If the designation of the quartzites south of the Last Chance fault 
in Silver Creek as Algonkian is correct, the amount of upthrust along 
the break in this region is upward of 1,000 feet. On the southern of 



120 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

the throe fissures to the west there is a minimum displacement of 600 
feet if the quartzites have been correctly assigned to the Devonian. 
while 400 feet may be attributed to the next. There arc no data for 
determining the amount of displacement upon the third. The Nora- 
Lily tunnel is upon the central of these three fissures, with the 
Devonian quartzite upon one wall and the lower shale of the Hermosa 
upon the other. 

These three fissures probably cross the river and reappear in the 
vicinity of the Lucky Pine or Calumet tunnel, which is probably upon 
the northernmost break. At this place there is a great deal of brec- 
ciation, perhaps due to a reunion of the fissures, the products of alter- 
ation occupying a zone fully 50 feel in width. A- in the case of the 
Nellie Bly fissure, these may have their representatives in some of the 
imperfectly explored quartz veins which cross the ridge al the head of 
Aztec Gulch. 

If. as suggested in the discussion of the relations of the fissures east 
of the Blackhawk fault, these are the eastward continuation of the 
faults of Silver Creek, it may well be that the Leila Davis, Alleghany, 
and Maggie veins correspond to the Last Chance fault, the great dis- 
placement of strata having been taken up in part by the Blackhawk 
break, hut having died out to some extent before reaching it. 

The extension of the Last Chance fault to intersection with the 
Blackhawk seems the most plausible way to account for the greatly 
increased dislocation <>n the latter south of Silver Creek; and if the 
fractures bounding the Aigonkian quartzites are later than the majority 
of the faults of the region, it might well he that the Blackhawk fault 
was already in existence, with a throw like that seen north of Silver 
Creek, at the time the Lasl Chance fissure was formed, and would thus 
naturally prove a line of weakness to which the major part of the new 
dislocation might lie deflected. 

Smelter fault. A fault of considerable local importance is shown 
on the ma]) crossing the lower -lop,, of Nigger Baby Hill in a direction 
N. 82°-84 I'.. This course carries il under the Grand View smelter, 
whence the name here given to it. The fault has not been observed 
in any distinct surface outcrops, bill its position i- e\ ident to within a 
very few feet, where the Devonian limestone comes close to the Algon 
kian schists above the smelter and a little higher, on the railroad 
switchback, where the lowest Hermosa strata are geen almost abutting 
against the schists, which are also exposed at the Futurity tunnel 
nearly 150 feet still farther up the slope. South of the Smelter fault, 
from the Devonian line to the Fate shaft, in Silver Creek, there are 
many exposures of the lower Hermosa sandstones and shales with 
strikes varying from east-west to \. 80 E. and with dips of between 
30 and 40 southerly, carrying them under the porphyry sheet shown 
on the map. 



cross a xd spencer.] . SMELTER FAULT. 121 

The eastward projection of the Smelter Vault carries it where a fault 
seems necessary on the south side of the Algonkian q.uartzites, which 

are exposed on the slope between the old Phoenix tramhouse and the 
Last Chance tunnel. If continued it would intercept the Last Chance 
fault near the mouth of Allvn Gulch. 

To the westward the Smelter fault would, if projected in a straight 
line, cross the Dolores and strike into the covered slope northeast of 
Iron Gulch, crossing the South Park fault about at the smelter. 
There is a possibility, as mentioned below, that a fracture connected 
with the Smelter fault does extend across the river in a direction 
south of west, but it seems certain that the main dislocation on the 
Smelter fault turns to the northwest at some point near the smelter 
and forms the southwestern boundary of the schist area above Pied- 
mont. It may be that the deflection to this course was caused by a pre- 
existing fissure— such as the South Park fault may be — but in any 
case the fault limiting the schists must be considered as in effect a 
part of the Smelter fault. 

The narrow band between the monzonite and the schists is very 
poorly exposed, but the Montezuma and other tunnels show that there 
is here a broad band of brecciated quartzite — a fault zone. Its gen- 
eral course is parallel to the fault line of the map. The quartzites are 
so brecciated that their structure can not be made out at any point 
seen, but they are in the normal position for Devonian quartzite, and 
are so colored on the map. If the structure is simple here the lime- 
stone of the Devonian must be cut by the monzonite, but outcrops of 
the contact were not found. The upper extremity of the schists is 
covered by gravel and slide rock, so that the union of the Smelter 
and Last Chance faults is entirely concealed. Broken lines across the 
slide area indicate the probable place of junction. 

The evidence that a fissure does exist on the northwest side of Iron 
Gulch, approximately in the course of the Smelter fault as it crosses the 
base of Nigger Baby Hill, is somewhat peculiar, and may be appropri- 
ately given in this place. The map shows a prospect at 9,375 feet a short 
distance from the gulch. On the slope directly above this prospect, at 
about 9,500 feet, a funnel-shaped sink in the surface soil and wash leads 
down to an open crevice in solid rock at about 12 feet from the surface. 
The crevice runs approximately east and west, has nearly vertical undu- 
lating walls, and is 2 to 3 feet wide where seen. A stone dropped into 
the fissure can be heard striking alternate walls after it passes out of 
sight and it is believed the fissure must be open to a depth of at least 
75 to 100 feet. No ore has been taken from the workings below, which 
are entirely in monzonite and are caved in. so that the crevice must 
apparently represent a landslide fracture or an open channel in a vein. 
Landslide phenomena are not notable on this slope of Darling Ridge. 

The dislocation on the Smeller fault below the Futurity tunnel is 
clearly several hundred feet, but can not he closely estimated because 



122 GEOLOGY OF THE KICO MOUNTAINS, COLOEADO. 

the upper limit of the -schist block — that is to say, the level at which 
the schists were overlain by the eroded Devonian quartzites — is not 
indicated by any known evidence. At other points upon its course the 
throw of the Smelter fault is still more problematical, as will appear in 
the next section. 

Gross faults between Smelter and Last Ghana faults. — The wedge- 
shaped area between these fractures is represented on the map as crossed 
by two hypothetical faults. Without reference to these this wedge is 
plainly a narrow block which has been thrust up several hundred or 
1,,000 feet, nearly in the center of the Rico dome. This band is so long, 
measuring- from the schists west of the river to the Blackhawk tram- 
house, that it does not seem reasonable to suppose that it could be thrust 
up in this manner without many cross fractures, and the rocks exposed 
in the area also indicate that transverse faulting has occurred. 

The western end of this block consists mainly of the Algonkian 
schists. They are known to extend as far east as the Futurity tunnel, 
which penetrates them for about l'»<» feet. Above the tunnel there 
are no further exposures for some distance. Hut at the Falcon 
tunnel, now inaccessible, the mouth of which is located on the fault 
line where it crosses the 9,250-foot contour, a great deal of common 
monzonite-porphyrj was encountered. The course of the tunnel is 
into the hill, almost north, and the porphyry apparently outcrops at 
its mouth. A vein and some ore was found at this place some years 
ago. hut at the time of visit no definite information could he obtained 
as to the workings. Porphyry debris covers the slope above the Fal- 
con tunnel in great abundance, and i- also present as partially covered 
talus eastward beyond the turn in the trail at 9,275 feet. It does not 
seem likely that all this porphyry debris can come from the mass 
above the Last Chance fault, and it therefore seems probable that 
a considerable porphyry body occurs between the Smelter and Last 
Chance faults from the end of the schist-,, somewhat above the Futurity 
eastward to the Algonkian quartzites. Hypothetical cross faults have 
therefore been represented on the map separating this supposed 
porphyry area from the schists and quartzites, respectively. It is 
not certain that porphyry i- the only rock in this subordinate block, 
nor are the courses of the cross faults definitely indicated by evidence. 

The quartzite of the eastern part of this block is cut by several 
veins, which may lie faults of gome importance. One of these veins 
crosses the slope a little above the Phoenix tramhouse with a course 
about X. 58 c W. A fine-grained porphyry dike in the quartzites is 
cut by this vein. 

South Park fault. — A comparatively minor fault-fissure is occupied 
by the South Park vein crossing Silver Creek. On the north bank 
across from the tunnel mouth the fault is very plain, for it brings 
porphyry against calcareous shales and gray sandstones. The strike 
is here N. 75 c W., and the dip N. 15 E. at an angle of nearly 80 , 



ckoss and spencer.] SOUTH PARK FAULT. . 123 

The general course of the fault is, however, much more nearly east- 
west, as determined at several places. It is occupied by a quartz vein 
throughout its known length. A tunnel on the north bank of the creek, 
perhaps 100 yards west of the South Park tunnel and running nearly 
north, strikes the fault vein 60 feet from the mouth, and in the stopes 
the fault is seen to be nearly east- west and almost vertical. This tunnel 
quickly cuts through the base of the porphyry sheet, revealing the 
sediments under it, dipping with the usual structure, and thus proves 
the dislocation on the South Park fault at this point to be about 50 
feet. The exact amount can not well be determined, for the base of 
the porphyry north of the fault is not well exposed. 

The fault runs just a few feet north of the little railroad cut in the 
ridge to the west. A shaft was sunk on it near by. In the railroad 
cut some mineralized shale beds on the north side yielded pay ore, 
but on following them into the bank they were soon cut off by the 
fault, beyond which was porphyry. 

On the western slope the dislocation of the porphyry sheet can be 
distinctly made out, and, less plainly, that of the Devonian limestone. 
One or two prospects on this side are on the fault or on veins parallel 
to it, but are too shallow to demonstrate which it may be. 

The course of the South Park fault must carry it to an intersection 
with the Smelter fault before reaching the river, but on the west side 
of the Dolores there is in all probability a profound faulting on a line 
N. 60° to 70° W., bounding the Algonkian schists on the southwest. 
This fault is considered as the Smelter fault and has already been 
described. 

To the southeast of Silver Creek the South Park tunnel follows the 
vein for about 500 feet, and beyond that point the fault is unknown 
either upon the surface or in prospect workings, unless one of the 
three prospects, now inaccessible, shown on the map between 9,300 and 
9,450 feet, may be upon it. With the multiplicity of veins occurring 
in this vicinity the assertion of such identity is hardly justifiable in 
the absence of definite evidence. 

The course of the South Park fault eastward would bring it near 
the western boundary of the Algonkian quartzite mass as represented 
on the map. But it can not be assumed that this fissure becomes the 
main fault on this side of the quartzites, for the reason that the Her- 
mosa calcareous shales, etc., come against porphyry at the mouth of 
the tunnel, as on the northwest bank of the creek, and hence the fault 
limiting the Algonkian quartzites must come down to Silver Creek 
somewhat east of the mouth of the South Park tunnel. The facts 
concerning the boundary of the Algonkian quartzites are presented in 
a later section. 

Area between the Smelter fault and Silver Creel-. — The western part 
of this wedge-shaped area Is quite simple in structure. The lowest 
Hermosa strata dip under the porphyry sheet shown by the map, and 



124 GEOLOGY OF THE EICO MOUNTAINS, COLORADO. 

appear to be underlain by quartzites of the same dip and strike. It 
has been explained in Chapter TT that the aye of these quartzites is 
more or less uncertain, and in the preceding section of this chapter it 
has been stated that they are traversed by several north-south veins, 
some of winch may have much greater importance as fault lines than 
appears demonstrable on present observations. 

To the east of these cross assures is a small triangular space con- 
cerning which very little is known, since the surface is almost wholly 
covered by soil and wash. It lies between areas of A.lgonkian quartz- 
ites, hut the evidence of prospecl shafts seems to prove that quite 
different materials must be present in this ground. A shaft just below 
the wagon road and less than 200 yards west of the railroad trestle 
over Silver Creek has penetrated a porphyry of dark-green color 
which is so much altered and so richly impregnated with pyrite that 
its character is not readily recognized. This i< probably a dike in 
Sediments similar to those of the next prospecl to be referred to. 
The shaft was inaccessible. 

Southeast of the above shaft, on the other side of the creek and 
helou the railroad, another shallow prospecl reveals -hal\ beds highly 
impregnated with pyrite and much altered to a dark-green material. 

The -haft u;h full of water and the structure at this point could not he 

ascertained. 

On the hank of the creek, midway between this point and tin- Rich- 
mond tunnel, is a -mall outcrop of marbleized lime-tone, in irregular 
and obscure contact with quartzite, in the stream bed. This marble 
resembles in some degree the Devonian strata in Rico, and this i- the 
only place in Silver Creek where any BUch material ha- been -ecu. 

In the Bertha tunnel, supposed to lie on the line of the Silver Creek 
fault, green pyritic material ha- been found similar in character to 
that at the prospect -haft, near the railroad tre-tle. and it i- notable 
throughout the Silver Creek area that the shales adjacent to veins are 

often mineralized in thi- manner. 

Silver Creek fault. Thi- name is applied t<> a fault which ha- not 
been -ecu. hut which it seems necessary to assume a- passing down 
the southea-t side of Silver Creek, from near the South Park tunnel, 
running just in front of the mouth of the Hibernia tunnel and thence 
down stream into Rico, as represented on the map. It- general course 
is apparently about N. 60 E., and the downthrow is on the south- 
eastern side, and is estimated at about 100 feet. The fault i- required 
to lower the base of the thick porphyry sheet of Newman Hill below 
the level of Silver ( 'reek. 

A thin remnant of porphyry cap- the ridge north of Silver Creek 
underneath gravels of probable glacial origin. Thi- is supposed to 
belong to the Newman Hill sheet, but the presence of porphyry in 
the railroad cut below, in irregular relation- to tin- -halo, renders this 
uncertain. 



cross and spencer.] SILVEK CREEK AND OTHER FAULTS. 125 

The porphyry sheet dislocated by the South Park fault between 

Silver Creek and the Grand View sin Iter is intruded in the lower 
Hermosa beds about midway between the Devonian limestone and the 
base of the Newman Hill porphyry. These relations are reasonably 
well proved by surface exposures and the developments in the Hiber- 
nia tunnel. 

This tunnel runs from its mouth 412 feet S. 14° E., all of the way 
in porphyry, and at this point connects with a shaft from the surface, 
also in porphyry, except for the surface materials. At the shaft the 
tunnel turns easterly with quite irregular course for a distance of 
about 750 feet. It remains in porphyry for s©me 500 feet from the 
turn, and then passes across the lower contact of the sheet into shales 
and thin-bedded sandstones with strike N. 55°-60° E., and a dip of 15° 
or 20° to the west of south, a normal structure for this part of New- 
man Hill. Passing on in easterly course, the tunnel penetrates another 
porphyry sheet, and at the extremit}^ of the workings, at the time of 
visit, the strata below that porphyry had been found. It is supposed 
that this lower sheet can be correlated with that on the surface north 
of Silver Creek. 

The evidence of the Hibernia tunnel is apparently substantiated in 
the workings of the South Park mine, but the great number of frac- 
tures revealed in this tunnel and the southerly drifts from it have so 
complicated the relations of the formations that it must be confessed 
that they are not entirely understood. But the presence of a minor 
porphyry under the main sheet is clear. 

The map represents this fracture as terminating at the South Park 
fault. It is true that a fault vein exhibited at the Bertha tunnel, near 
the Richmond, is about in the line of the Silver Creek fault, but the rup- 
turing on that fissure appears to be a part of that by which the Algon- 
kian quartzite block on the southeast was thrust up. 

Fdidtshoiindliuj tin- (jtiiirf-^/tr mas* south of Silver Creel:. — The mass 
of Algonkian quartzites rising from Silver Creek to a height of 450 
feet above the stream and extending from the Laxey tunnel southwest 
for about 1,200 or 1,300 feet is regarded as a block surrounded on all 
sides by faults. But so completely are the boundaries of the mass con- 
cealed by surface materials that very little direct evidence of the exact 
position of the faults can be obtained. At the Laxey tunnel the east- 
ern boundary of the quartzite appears as a fault vein, the general 
course of which is N. 15° W. To the east of this fault appear sand- 
stones and shaly beds of the lower Hermosa, Avhich extend eastward 
into Allyn Gulch, appearing at the mouth of the gorge below the 
porphyry sheet. To the west of this line quartzite outcrops extend 
well down toward Silver Creek. 

From the Laxey tunnel southwest the massive quartzite exposui*es 
are bounded by slide rock, chiefly of monzonite-porphyry, at a level 
above 9,500 feet. As this is the normal position for the Newman Hill 



126 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

porphyry .sheet, and no other important body of that rock occurs on 
the slopes above until the summit of Dolores Mountain is reached, it 
seems certain that the upper boundary of the quartzitea is near the visi- 
ble limit of the outcrops and must be a fault with a throw of 600 or 
800 feet at least. 

At the southern extremity the line between porphyry and quartzite 
is closely defined though not actually exposed. It gradually descends 
the slope and is nearly in line with the South Park fault, as has been 
mentioned in describing that break. Hut from the Fact that the Car- 
boniferous strata are seen at the mouth of the South Park tunnel with 
the structure exhibited to the north of the creek, it must be concluded 
that the necessary fault bounding the Algonkian quartzitea reaches the 
creek level above the mouth of the tunnel. It is probably within a 
hundred yards of the tunnel, w here surface debris comes down to the 
creek level, and the system of fissures noted in the Algonkian quartz- 
ites from the Richmond tunnel down to the limit of the outcrops may 
be regarded as in general parallel t<> this fault. 

The hypothetical fault separating these quartzitea from the supposed 
Devonian area north of Silver ('reck i- necessary because there is no 
indication <>f any structure which could possibly briny those quartzitea 
over the Algonkian area. The vein followed by the Bertha tunnel, a 
little wot of the Richmond tunnel, i- assumed to be on this fault line. 

To the southeast of it tin- quartzitea arc brecciated and sheeted in a 
inc-t marked degree. 

Telescopt Mountain fault. A great fault, the course of which, as 
shown on the map. is -oniew hat hypothetical, must cross tin- ridge from 
Telescope Mountain to Nigger Baby Hill at about 11,500 feet and run 
in a general westerly direction down the slope along the southern line 
of C. H. C. Hill. It is possible that the faulting is not upon one fissure, 
as represented, but rather upon a fault /one. A part of the existing 
structure may also be due to steep dips, a- will be explained below. 
but the observations made are too meager to justify the representation 
on the map of anything but the simple hypothetical fault. The total 
dislocation to lie accounted for amounts to between t, 750 and 2,000 
feet, a- indicated by the considerations to be presented. 

The Rico formation crosses the west -lope ,>f Nigger Baby Hill with 
a dip which will carry it against the hypothetical fault of the map at 
somewhat below the level of 9,750 feet A ledgeof massive blue Ilei- 
mosa limestones, outcropping near the Premier mine, occurs at this 
level; hence it is plain that a break amounting to the thickness of the 
Rico formation (300 feet) plus tin- upper division of the Hermosa ( li'ii 
feet) and an unknown amount of the massive limestone series, a total 
which may exceed 1,000 feet, must exist in the covered space south of 
the limestone outcrops. 

The map shows that the Rico bed-, reappear in the cliffs of Telescope 
Mountain at about 11,000 feet, here possessing a northerly dip, which 



cross and spencer.] TELESCOPE MOUNTAIN FAULT. 127 

would bring them onto the southwest ridge of Telescope Mountain at 
somewhat above 11,250 feet. The landslide area of this ridge unfor- 
tunately extends much above this level, but, as exhibited by the map, 
there is an area of exposures on the western slope surrounded by land- 
slide debris. The strata of these outcrops are greenish shales and 
sandstones with light-colored grits, and can belong only to the upper 
part of the Hermosa. The Rico beds must, then, actually reach the 
crest of the Telescope Mountain ridge at about 11,500 feet, and the 
great fault limiting them on the south must cross the ridge nearly as 
represented, and throws them down about 2,000 feet to their position 
south of C. H. C. Hill. 

That a fault of much importance crosses the southeastern face of 
Telescope Mountain is furthermore evident from the great apparent 
thickness of the Dolores Red beds here present. From the summit of 
Telescope Mountain to the base of the Dolores formation in Silver 
Creek the difference of level is about 2,250 feet, and as the strata have 
a general northerly dip of 10° to 15° all the way up the slope, this 
represents an apparent thickness of nearly 3,000 feet of Dolores 
strata. Moreover, the horizon at the summit of the mountain is some 
600 feet below the top of the formation, as shown by the situation of 
the Rico beds on the western slope in the strike line. The apparent 
thickness of the Dolores formation, therefore, reaches nearly 3,600 
feet, if no fault is taken into account; and as this is just about double 
the real thickness, there is a dislocation, or a series of dislocations, 
crossing the southeastern slope of Telescope Mountain amounting to 
nearly 1,800 feet by this measurement. It is plain that if there is a 
single fault with a throw approaching this amount it must be situated 
very near the line adopted, to avoid the appearance of the La Plata 
sandstone on the south and of the Rico formation on the north. 

Three lines of evidence thus agree in indicating the general course 
and the amount of this important dislocation. The fault of the map 
is made to coincide with a quartz vein discovered on the southeast 
slope of Telescope Mountain, traversing Dolores Red beds, but in the 
nature of the case it is impossible to measure the dislocation in the 
midst of this great series of alternating beds of similar character, 
without perfect exposures, and this slope, while steep and presenting 
many cliff outcrops, is largely grassed over. The vein in question is 
exposed in two or three shallow prospects, and in them courses 
N. 80° E. and has a northerly dip of about 60°. Its eastern projec- 
tion must apparently run between two porphyry masses, the lower of 
which is crosscutting and approaches so near to a more regular sheet 
above that if the strike of the fault did not cany it through a small 
covered space between them, the two porphyries might reasonably be 
supposed to unite. 

The Hermosa shales and sandstones of the isolated exposures on the 
western slope show that there is much Assuring and that reverse dips 



128 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

prevail, at least locally, in the area just north of the hypothetical fault 
line in the region obscured by landslide debris. Several veins traverse 
this block, and one of them is a fault X. GO E.. nearly vertical, and 
with a displacement of more than 00 feet, though the direction of 
downthrow was not determined. Several caved tunnels indicate other 
veins in this mass. The structure is quite at variance with that normal 
to Telescope Mountain above or to the ridge <>n the south. In the 
northernmost outcrops the strike is nearly N. 80 E., and the dip is 
southerly, varying from •'! to L5° in different exposures. Toward the 
south the strike swings to nearly northwest-southeast, and the dip 
reaches an observed maximum of .".."> SAN'. Irregularities similar to 
those just mentioned could not be detected in the Red Iteds on the south 
slope of Tele-cope Mountain, and it is therefore quite possible that 
northwesterly fissures, in general parallel to the Blackhawk fault, limit 
the structures seen in the area of Hermosa strata above mentioned. 

The western extension of this fault passes into the obscured area of 
Darling Ridge, and even more than in the cases of (he Nellie Bly, Last 
Chance, and Smelter faults there is no known evidence showing the 
manner in winch it dies out. It may We cut off in its principal dislo- 
cation by other fault-. So far a- the structure of Darling Ridge is 
exposed by mine workings, there i- no suggestion of any great dis- 
placement north of A/tec < rulch. 

Faults of G. II. < : Hill. It has been suggested that the Blackhawk 
fault traverses the landslide-covered area of C. II. C. Hill to a union 
with some one or more of the faults known near Burns. It is also 

probable that other fissures upon which there has been i e or less 

dislocation cross this space nearly parallel to the Blackhawk fault. 
Some one of these faults may represent the northeast boundary of .he 
landslide, parallel to the notable line of cliffs seen in Pis. KV-XVIL 
A slickensided surface seen at aboul L0,750 feet, at the base of these 
dill's, may represent such a fissure. 

But the evidence of nearly continuous ore deposit-, which are in 
general parallel to the bedding through a large pari of the middle area 
of the hill, proves that no gieal amount of faulting can exist except 
in the region of the great Telescope .Mountain fracture. 

Faults of northeast-southwest trend cross the northwest ridge from 
Telescope Mountain and doubtless extend some distance under the land- 
slide debris. 

Othe?' faults. — The remaining faults of the area covered by this 
special map possess no marked importance not sufficiently indicated on 
the map. They are found in all directions from the center and run 
with various courses. Beyond the Rico Mountains proper faults have 
been noticed, particularly to the west and northwest. Nearly west of 
Eagle Peak a fault of about 500 feet crosses the West Dolores River 
nearlv east and west. 



CHAPTER V. 
LANDSLIDES. 



By Whitman Cho 



GENERAL STATEMENT. 



For .several miles about Rico in nearly all directions there has been, 
in Pleistocene time, a great deal of landslide action of a character 
rather peculiar to this region. As a result of this extensive move- 
ment the physiography of certain tracts has acquired characteristic 
details and the normal geologic structure has been more or less com- 
pletely obscured. The movements in question have taken place since 
the valleys and mountains received their general form and relations as 
now seen, but. although subordinate and modifying slips have repeat- 
edly occurred down to the present time, the greater part of the phe- 
nomena probably date back to early Pleistocene. 

While some of the slide areas embrace square miles of surface, the 
action seems to have been much more superficial than the landslide 
movements of the neighboring Telluridc quadrangle, described in the 
Telluride folio. Even in the most continuous areas there is seldom 
evidence of large bodies having moved en masse, but there seem to 
have been many distinct slides, which, through disintegration by 
various agencies, have come to grade into one another and thus to form, 
a confused mantle of fragments! material covering the solid rock. As a 
whole the landslide phenomena constitute one of the most important 
elements in the local geology. To them is due the absence of clear 
geologic structure in areas adjacent to those in which the formations 
are most plainly exposed. And even with the most careful examina- 
tion there are some considerable spaces within which the structure of 
the underlying formations can be ascertained only by the aid of tun- 
nels and shafts driven in the course of the mining development of the 
district. 

In the past prospecting of the Rico Mountains the failure to recog- 
nize the true significance of (he Landslide phenomena and to perceive 
their extent has led to very great loss of time, labor, and money. 
21 GEOL, it 2 '•> [29 



130 GEOLOGY OF THE RICO MOUNTAINS, COLOEADO. 

The first recognition of the landslides, in the course of this survey, 
was made by Mr. Purington, while he was engaged in the preliminary 

work on the ore deposits in the summer of 1896. 

ENUMERATION OF LANDSLIDE AREAS. 

The town of Rico lies nearly in the center of the district character- 
ized by landslides. The largest continuous slide areas are in the val- 
ley of Horse Creek, and they extend far up the northern and southern 
slopes. On the northern side a slide surface extends from the creek 
bottom to an elevation of nearly 11,400 feet toward Sockrider Peak, 
including Sinbad Hill. On the south side almost the entire surface 
from the south fork of the creek eastward to the end of Darling Ridge 
is obscured, as to its structure, by landslide material. The crest of 
Darling Ridge is shattered and superficially dislocated along almost 
its entire length from the Uncle Remus claim to the river. 

The north side of Burnett Gulch presents little but landslide phe- 
nomena from an elevation of 1.1,250 feet on Expectation Mountain to 
the mouth of the creek. Wesl of the town of Rico there are small 
areas of landslide contiguous to the ridges above named, but associated 
with common slide or wash and other surticial masses. 

The eastern mountains of the Rico group, south of Silver Creek, 
exhibit landslide action in numerous places, to be described, but no 
large areas are there found. Dolores Mountain, Blackhawk Peak, 
Whitecap Mountain, and other localities present small landslide areas 
of more or less distinctness. Newman Hill has received fragmental 
material of this origin from the higher -lopes of Dolores Mountain, 
but the mingling of surticial masses of different origin is here so 
complex as to subordinate the importance of the landslides. 

Telescope Mountain and the slopes of Nigger Baby and C. II. C. 
hills have suffered some of the most extensive landslips of the region, 
the present topography of C. H. C. Hill being hugely a result of this 
movement. 

Beside these larger areas there are many others, somewhat farther 
removed from Rico, in which landslides of limited extent haveoccurred. 
Stoner Creek, Landslip Mountain, and the ridge east of Whitecap 
Mountain are the most important of these. 

NORTH SIDE OF HORSE GULCH. 

The principal landslide area on the north slope of Horse Gulch is 
represented on the map. It is one of the most clearly defined slips of 
the region and has very characteristic details of topography. In PI. IX 
is given a view of this slide area as seen from Sandstone Mountain. 
On the right hand are seen the normal ledge outcrops of massive 



cross] LANDSLIDES IN" HORSE GULCH. 131 

Dolores and Rico strata, which are suddenly interrupted on the line of 
a ravine coming down to Horse Creek just above the Puzzle mine. 
From this ravine westward the slope possesses the irregular features 
of knoll, ridge, trench, and hollow of various shapes, found on all the 
landslide surfaces, and exhibited in some measure by the illustration. 
The general contrast between this area and the adjacent slopes is very 
striking from all points of view. 

The greater part of this slide area is now covered with grass or an 
aspen growth, and the direct evidence as to the character or attitude 
of the formations beneath is found in local outcrops, small slides of 
recent date within the main area, the prospect holes, or the physio- 
graphic details found by observation to be characteristic of landslide 
surfaces. Along the landslide bank of the ravine, on the eastern bor- 
der and below the level of 10,050 feet, the loose materials have at 
several places been washed away, revealing ledge outcrops of greenish 
Hermosa sandstone. These exposures belong to different blocks, 
some of them 50 feet in visible length, the strike and dip changing 
abruptly from block to block, and never corresponding to the normal 
structure found on the east side of the ravine. Some of the blocks 
show a nearly vertical dip, while in others the beds dip -i0 o or more, 
usually clown the slope. 

In the view shown in PL IX may be seen a bare spot, -100 or 500 feet 
above Horse Creek, which is due to the recent falling away of a part 
of what was doubtless a wooded or grass} r slope like that above and on 
either side. In this way a jumble of formations has been exposed, which 
is probably typical of the relations existing in much of this slide mass. 
The exposure reveals ledges of much-shattered sandstone, shale, and 
porphyry, dipping in most widely varying directions. The change 
from one block to another is abrupt, by a fracture or crushed zone, 
and the original relation of the various formations to one another can 
not be definitely ascertained. Porphyry predominates along a zone 
at the top of this exposure, and the first inference is that there is a 
sheet of porphyry here which may be traced for some distance, but in 
fact several structural phases of porphyry are here mingled, and it is 
questionable whether any one sheet can be identified at this locality. 

This exposure serves to illustrate the manner in which the complex 
of a slide area gradually disintegrates still further, and must eventually 
lose all its distinctive features. Through the shattered condition of 
such landslides they become saturated with water, and at times differ- 
ent portions will slump away and break up into a mass of ordinary 
avalanche or slide material. Each fresh break furnishes a point of 
attack for the elements of frost, rain, springs, snowslides, etc.. and 
the destruction of the shattered mass goes on more rapidly. 

All over the central part of this landslide area there are very marked 
knolls and ridges, with shattered and irregular rock outcrops, back of 



132 GEOLOGY OF THE RICO MOUNTAINS, COLOEADO. 

which are the V-shaped trenches marking- the fracture lines of individ- 
ual slide blocks. These are almost always partially tilled in, and fresh 
fractures in the soil are rare. The trenches are so independent of any 
normal drainage system that their origin seems open to no question. 
Some of them are shown on the map. but any adequate expression of 
this topography would require a much larger scale and a contour inter- 
val of 25 feet or less. Hollows without drainage outlet are common 
on the lines of trenches, some of them being shown by the map. 

The prospect tunnels or shafts which have been run into the land- 
slide area all show greatly disturbed strata, and most of them were 
caved in at the time of visit. It is safe to say that none of them pene- 
trated to solid rock in place beneath the slide. Exception may he 
made in the eases of some of the tunnels starting near the borders of 
the slide area, which probably run under the fragmental slide debris. 

Along the base of this landslide area the common wash and talus 
obscure the actual limits of the slide, hut it probably extended quite 
to the creek bed. On the wesl it is apparently bounded by the ridge 
east of the gulch heading under Sockrider Teak, although hut few 
solid outcrops exisl near the line drawn on the map. The eastern limit 
is sharp for the greater distance, but becomes lost above in the accu- 
mulations of debris from snowslides and other agencies. 

The landslide area ends upward in a point under the cliffs of red 
Dolores sandstones at about 11,400 feet. Chaotic slide blocks, which 
are rounded and more or less grassed over, cease at about 1 1,000 feet, 
and between this and the solid cliff line there is a small area of more 
angular blocks of red sandstone and porphyry in which there IS often 
a dip toward the mountain. Each of these blocks is clearly marked, and 
fissures of dislocation between them are like open faults with a meas- 
urable throw of 50 feet or less. Some of these blocks have fallen 
from the cliff in comparatively recenl time, and fissures which may 
Serve a- boundary cracks of future slips are to be found here and there 

in the cliff. 

SOUTH SIDE OF HORSE GULCH AND DARLING RIDGE. 

The area from the bed of Horse Creek t<> the crest of Darling 
Ridge and from the south fork of the creek to the Dolores River 
contains so few outcrops of rock in place that it may be treated as 
one landslide area. No other section illustrates 80 well the conception 
to be presented as to the origin of the landslides of the Rico 
Mountains. 

Crest of Darling Bidge. The formations of the crest of the ridge 
are obviously not derived by sliding from any other source, but they 
are in many places so shattered by important fractures running in all 
directions, and the blocks bounded by these fractures are so plainly 







- 


; 


i fife 


flm^l 



cross.] LANDSLIDE AREAS NEAR DARLING RIDGE. 133 

dislocated superficially that the whole muss may be considered as 
broken and not strictly in place. The best illustration of the shatter- 
ing is in the massive stock of monzonite opposite the head of Iron 
Gulch. By a glance at the map it will be seen that there are here a 
number of sharp pinnacles and knolls, to which one or two contours 
have been given. But a map of this scale fails to show the number 
of these knobs, and the hollows, curving ravines, and irregular depres- 
sions between them, belonging to no drainage system. The rock of 
the knobs is often fresh, but much shattered, and the hollows between 
are rounded by the gravel of disintegration washed into them. This 
topographic detail, while on the top of the ridge, is similar to that 
on the landslide slopes. Below these pinnacles on the slope to Horse 
Creek are some other knobs of monzonite, and the surface is covered 
by talus and landslide heaps nearly all the way to the creek bed. 

Eastward from the principal area of monzonite, along the crest of 
the ridge, there occurs a tongue of sedimentary rocks, then a second 
and smaller area of monzonite, and below that a great series of strata 
with intrusive porphyries. At several points the primary boundaries 
of these formations are more or less clearly exposed, and, as represented 
on the map, it must be assumed that the normal geology of this ridge 
would show the Hermosa and Rico formations including several por- 
phyry sheets, and all penetrated by a single branching stock of mon- 
zonite or by two distinct masses. But from the crest, or near it, down 
to Horse Creek the surface is a mingling of landslide blocks, large or 
small, intact or in process of dissolution, and geological boundaries 
showing the original relations can not be traced. 

The slope below the monzonite of the crest is mainly covered with 
this rock. Sediments and porphyry are mingled with the monzonite 
over a considerable space, but practically no monzonite occurs east of 
the ravine heading opposite the easternmost exposure of monzonite on 
the ridge. The mingling is not as in ordinary talus below cliffs. A 
knob or ledge at one point is perhaps wholly of one rock, or of sand- 
stone with a porphyry sheet, while an adjacent knoll is equally pro- 
nounced of monzonite. 

Physiography of the slop,'. — The general physiography of this ridge 
is seen in PI. X. Its features are not large enough in most parts to 
allow satisfactory expression with 50-foot contours. The main feature 
is the great number of trenches, most frequently parallel to the con- 
tours, or near it, yet often running diagonally across the slope. As a 
rule no trench is persistent for a long distance, being cut off b\ r some 
other trench. A few of these lines are ravines of importance, shown 
by the maps, and at several places they run up to or cross the crest of 
the ridge. 

Outside of the trenches are mounds, knobs, furrow-like ridges, or 
benches, and in these are not infrequent ledge outcrops which by vari- 



134 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

ous dips and strikes and the shattered condition of the rocks add to the 
evidence of landslide action. PI. XIII represents one of the character- 
istic trenches, at an elevation of about 10,500 feet, between the south 
fork of Horse Creek and the head of the "blowout." Many of this 
character exist on the adjacent steep slopes. Beyond the trenched 
surface part of the uneven profile of Darling Ridge is seen, and in the 
distance Telescope Mountain and the upper part of C. H. C. Hill. 

From elevated points on the north side of Horse Creek with a favor- 
able light one can count 25 or 30 lateral trenches, similar to that of 
PI. XIII, on many section lines between the creek and the crest line of 
Darling Ridge. No regular drainage channel exists on the south side 
of Horse Gulch between the river and the ravine opposite Sinbad Hill. 

On the slopes between the trail leading to the Magnetite mine and 
the lower part of Horse Creek there are many outcrops showing mas- 
sive fossiliferous limestone and associated sandstone. Some of these 
are extensive enough to suggest that they represent rock in place. 
The prevailing structure in these outcrops is a gentle dip down the 
slope, liut the abrupt changes in dip and in character of rocks, with 
the presence of the usual trenches back of or diagonally crossing the 
slopes, make it clear that no one ledge examined can safely lie consid- 
ered as in place. It is probably true that in some cases, especially on 
the higher slopes, the dislocation is not very great, but it is sufficient 
to make correlation of different outcrops very uncertain except upon 
a basis of exhaustive study of the whole ridge. 

Liutddnlr hlocl- at tin f'nzzl( mine. That there has been landslide 
action in Horse Gulch has been evident to all familiar with the ground 
about the Puzzle mine and with the experience of those who have 
tried to find the continuation of the ore body originally disc overed in 
the Puzzle. But the extent of the slide has not been appreciated. 

The view given in PI. XIV shows in detail the character of the bench 
in the valley where the original discovery of the Puzzle ore body was 
made, and in PI. X may lie seen the general relations of the locality 
to the landslide surfaces alreadj discussed, on both sides of the creek. 

The ore body of the Puzzle mine, a replacement of a limestone 
stratum by galena, etc.. was found in a ledge outcrop facing the stream 
bed, on the right hand of PI. XIV. and opposite the buildings shown in 
the illustration. The strata of the ledge included crinoidal limestones 

typical of the middle divisi f the Hermosa Carboniferous. The 

beds have a general dip downstream, but they are irregularly dis- 
located on fissures now open, and in places the dip is southerly at a 
low angle. The structure is at variance with that normal to the gulch, 
as seen on the north side. 

The ore was traced under the bench, but it was soon cut oil by breaks 
on the east, south, and west. A shaft sunk in the little trough at the 
base of the snow-covered slope, near the building shown in PI. XIV, 



S. GEOLOGICAL SURVE 



TWENTY-FIRST , 




DETAILS OF LANDSLIDE TOPOGRAPHY IN THE AREA ON THE NORTH SIDE OF HORSE GULCH. 
Photograph by Cross. 



cross.] THE BLOWOUT. 135 

passed into stream gravels at a depth probably loss than 50 feet, prov- 
ing that this ore-bearing block has slipped down from the slope above. 

A few yards to the west of the break limiting the ore in the main 
Puzzle workings a continuation of the ore body was found in the Puz- 
zle Extension and traced, with several small dislocations, to a more 
extensive fracture, beyond which the present developments have failed 
to discover it. A similar ore-bearing horizon has also been formed in 
the M. A. C. mine on the east, but so limited by cross fractures, includ- 
ing apparently old faults, that the identity of the ore bod}' with that 
of the Puzzle mine is open to question. 

The workings on the original Puzzle ore body, the efforts to trace it 
beyond the breaks on all sides, and the surface configuration of the 
gulch slope, all give evidence that there has been complex shattering of 
the strata in this vicinity, and that the formations thus far penetrated 
in the prospect tunnels and shafts are in rather small and irregular 
landslide blocks. Nothing as yet discovered indicates the depth to 
which this superficial dislocation extends, nor the position of the for- 
mation in place from which the ore-bearing block of the Puzzle mine 
was detached. 

k * Tin- Blowout." — Another locality in Hoi'se Gulch worthy of special 
description is the so-called "blowout," situated on the southern slope 
between 10,000 and 10,500 feet, and north of the monzonite pinnacles 
of Darling Ridge. The map shows closely spaced contours in a drain- 
age channel at this point and a curving ravine above it, heading 
between the two monzonite areas of the ridgecrest. In fact, this ravine 
heads on the' flat top of the ridge, and is but one of several very marked 
landslide trenches in that neighborhood. The trench shown in PI. 
X1I1 runs eastward to the head of the blowout. 

The main blowout means in this case, as in many others, a locality 
of intense mineralization of the rocks, followed by decomposition and 
oxidation and hj'dration of the ore particles, mainly pyrite, producing 
strong coloration of the rocks as now exposed. The existence of the 
blowout at this particular point is due to local erosion revealing an 
internal condition of the rocks which is not local but extends for some 
distance along this slope. The nature of this erosion is shown b} r some 
smaller adjacent exposures, where loose f ragmental material has become 
softened by springs and lias given way, flowing as a mud stream down 
the steep slope, leaving a hollow, which must rapidly enlarge once the 
point of attack for frost and running water has been developed. Below 
the main blowout a fan or alluvial cone of abnormal size indicates a 
rapid transfer of material. 

Examination of the rocks exposed at the blowout reveals the presence 
of monzonite and syenitic porphyry in so confused a relation that, with 
the complications resulting from landslide action and the intense alter- 
ation, it is impossible to trace either rock except by fresh fracture at 



136 GEOLOGY OF THE KICO MOUNTAINS, COLORADO. 

every step, so that no positive statement can be made as to the original 
rock in place at this point. From study of the best exposures in this 
vicinity it appeals probable that there is here a stock of monzonite, 
with associated porphyries, penetrating sediments which contain intru- 
sive sheets of the common porphyry of the region, and thai still 
further complication may be due to cross-cutting porphyry masses 
connected with the eruptive center at the folks of Horse Greek. 

Western limit of the landslides. The western limit of the continuous 
landslide area on the southern slope of Horse Gulch is rather indefinite, 
but lies on the east side of the south fork. It IS here obscured by the 
presence <'( surficial materials of later origin, part of which are derived 
from the head of the south fork, while other portions are the result of 
disintegration of the landslide Mocks. Hut from the edge of the por- 
phyry cliffs of the little canyon it is only a short distance up the slope 
to trenches and other physiographic features of landslide origin. 

The southern limit in the south fork is the line of the map running 
down from the -addle near the Uncle Remus. 

The force by which the rocks of Darling Ridge were x. shattered, 
producing the fissures which limit the main landslide blocks, was also 
exerted iii less degree to the w e-I w a id. and landslides of small size 
have taken place in the angle between the south and wesl forks of 
Borse Creek, on the end of the ridge from Anchor Teak. The child' 

evidence of this action i- in i v or less distinct trenches of general 

east -W681 direction, below which the strata are broken up and disturbed 
in strike and dip. 

TELESCOPE MOUNTAIN AND C. H. C. HILL. 

The area embracing Telescope Mountain and that part of its western 
slope know n a- < . II. ( '. Hill contains some of the most distinct land- 
slides of the district. \ et presents in them the clearest evidence as to 
the superficial character of the phenomena. The movement Is still in 
progress at certain points. The slides have greatly hindered the eco 
noinic exploration of this tract, and have effectually concealed certain 
structural features which are of great importance to the understanding 
of the geology of the Rico Mountain-. Several of the important fault 
lines whose presence is assured <an not be well defined until mining 
operations expose the structure in the solid rock beneath landslide 
masses of unknown depth. 

Telescop< Mountain. The structure of the upper part of Telescope 
Mountain is very clear, from the excellent exposures of the red Dolores 
strata on the summit and for some distance down the ridges leading 
out in various directions. On the west and ,-outhwest the manner in 
which superficial landslide- obscure the geology is well illustrated. 

The summit of the mountain is made up of crumbling red sand- 
stones with a dip toward the im.mIi. and while the beds do not form 



cross LANDSLIDES ON TELESCOPE MOUNTAIN. 137 

prominent outcrops some of the principal beds can be traced nearly 
around the peak. On the northwest ridge some variations in strike 
occur, which may be due to ill-exposed minor faults, but at about 
12,000 feet the rocks outcrop in blocks which are separated by open 
crevices and the tilting in different directions shows superficial dislo- 
cation. From about this point a large amount of avalanche material 
has fallen down the northeast slope into the head of MeJunkin Creek, 
and a less amount westward to C. H. C. Hill. Increasing evidence of 
minor fractures and dislocations is found farther down the ridge, and 
about where the fault crosses, at 11,600 feet, there is much confusion, 
large and small blocks lying in chaotic relations. There has been 
more o]' less land-slipping all along this northwestern ridge, but it is 
insignificant beside that within the designated areas of the map. 

The western face of Telescope Mountain is shown in PI. XV. 
which brings out the characteristic landslide topography in contrast 
with the normal. On the left hand is the cliff which faces C. H. C. 
Hill all the way from a point under the summit of Telescope Mountain 
to the Dolores River. This cliff is interrupted a little southwest of the 
summit by an avalanche path from the head of the landslide area. 

This apex of the landslide is at 11,800 feet, just below ledges of an 
encircling porphyry sheet. Here are knobs of Dolores sandstone 
tilted in all directions, some of them almost ready to follow the well- 
worn track of many predecessors, which leads far down the slope. 
Blocks so small as those now poised break up into avalanches as the}' 
fall and do not reach any great distance, but in the past the slope has 
been such or the falls have been of such magnitude that the trail of this 
red material can be followed to the river. 

From the same level of 11,800 feet the slides have descended south 
and southwest toward Silver Creek or down the ridge toward Nigger 
Baby Hill. But this fall has been less in volume and on the south 
slope the material has disintegrated and has become grass covered and 
smoothed out. But the line between the cliffs below and this landslide- 
surface is very distinct, running along at about 11,000 feet. On the 
crest of the ridge there is the usual landslide topography, especially 
for several hundred feet heiow the ledges of porphyry just above the 
slide area. 

C. II. ('. Will. — The triangular space between the Dolores River, 
the southwest ridge of Telescope Mountain, and the cliff line, seen in 
PI. XV, is known as C. H. C. Hill. It is really a broad hollow on 
the slope of Telescope Mountain. Its character and relations are 
shown in Pis. XV and XVI. In the former view the peculiar physi- 
ography of the surface is well expressed, and in the latter the relation 
to the Dolores Valley may be seen. 

"While the landslide trenches, ribs, and knolls are very plain over 
Dearly the entire area of C. II. C. Hill, the examinations have shown 



138 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

that the landslide phenomena are, on the whole, much more superficial 
than might reasonably be inferred from the physiography. The 
peculiar topographic features of the hill are principally due to land- 
slides, but the ground, which has slipped in blocks, has been in part 
covered by avalanche debris and common talus. The disintegration 
of crushed rocks has yielded soil, and over much of the hill a growth 
of spruce and aspen conceals everything. 

The part of the hill in which normal landslide phenomena are now 
most distinct is a broad band parallel to the cliffs on the northeast. 
The most pronounced trenches run in general parallel to these cliffs, 
and it seems probable that an observed sheeting of the strata in a north- 
west-southeast direction has caused not only the cliffs of to-day but 
numerous fissures bounding thick plates or blocks of rock which have 
fallen en masse at various times. At one place observed, the present 
cliff exhibits a very distinctly polished and striated surface, which may 
be due to landslip action. 

In the zone below the cliffs there are a Dumber of knobs or knolls 
on which are outcrops showing the composition of the mass. Most 
commonly a complex of huge blocks is found, which may be in chaotic 
relations or may have a rude correspondence in dip and strike, though 
assures of small dislocation run through in irregular manner. The 
strata of Such B knoll are either predominantly of one kind or clearly 
belong to one part of the sedimentary series. One of these promi- 
nences, showing mainly limestone, is situated just south of the Pigeon 
Mine. As the higher clitls above the Pigeon are of the upper sand- 
stones and -hales of the 1 [ermosa Carboniferous, it is evident that this 
block lias not slid tar down the slope, but the shattered condition of 
the limestone Ls testimony that it has undergone the disturbing action 
of the landslip period. 

In PI. XVII is shown one of the knolls of landslide origin, with a 
sink and bench back of it. the cliff representing either the face from 
which this slide came or one back of the cliff of the slide epoch. 

Damming of Dolores River. The bench between the wagon road and 
the river, extending from Burn- to a point below the mouth of Horse 
Creek, is probably composed entirely of landslide material. As shown 
by the ma}), the river for some distance above Burns Hows over a very 
tlat. broad bottom. Immediately below Burns the stream passes into 
a little gorge, bounded on the western side by cliffs of limestone and 
sandstone and on the east by a steep bank made up of limestone, sand- 
stone, and conglomerate, in a wholly confused mass of coarse slide. 
No outcrops of rock in place occur on the eastern side along the face 
of this bench, and the railroad cutting reveals most clearly the chaotic 
mingling of various rocks. In PI. XVI is an illustration of the abrupt 
ending of the flat at Burns against the bench of landslide material. 

It seems necessarv to assume that the present alluvial flat at Burns is 



cross] RECENT SLIDES ON C. H. C. HILL. 139 

due to the damming- back of the river by the slide, but it also appears 
probable that at the time of the slide the valley bottom was broad and of 
very gentle grade along the stretch now occupied by the slide bench. 
From the mouth of McJunkin Creek to the beginning of the gorge 
below Hums, u distance of 1£ miles, the river has a fall of but 50 feet, 
while between Burns and the mouth of Horse Creek the fall is 150 feet 
in two-thirds of a mile. It is probable that before the slide the grade 
of the river was very even from McJunkin Creek to Silver Creek. 

The excavation for the wagon road from the flat at Burns to the top 
of the slide bench, seen in PI. XVI, exhibits the transition from the 
almost undisturbed strata near the bridge to the confused mass of large 
blocks forming the bench. As far as the C. V. G. tunnel, just below 
the road, the succession of greenish sandstones, shales, and occasional 
limestones is like the sequence known above the main limestone series. 
At about the tunnel a more disturbed condition appears, and becomes 
more and more pronounced southward to the ravine at the bend of the 
road. While the general strike of the beds continues the same the dips 
are variable, cross fractures, with evidence of dislocation, are common, 
and there has been slipping, especially on shale layers. Shearing move- 
ment, by which certain strata are obliquely cut off, is evident, and cor- 
relation of beds from place to place becomes uncertain. From the 
bend in the road on to the bench and along the latter there is a chaotic 
mixture of limestone, sandstone, and porphyry, the dips of the larger 
exposures being generally into the hill at various angles. 

At the southern end of this slide bench, opposite Horse Creek, the 
exposures are of finer debris, and it is probably the accumulation of 
detritus by avalanche and ordinary slide, partly from far up the slopes 
of Telescope Mountain. 

Recent slipping m C. If. G. Hill. — Evidence that motion is still in 
progress in the surface materials of C. H. C. Hill is abundant in the 
prospect tunnels and shafts of various places through the crushing or 
the twisting of timbers. But the best proof and illustration of the 
character of this movement is seen in a crevice now gradually opening 
at the upper end of C. H. C. Hill. This crevice extends from an alti- 
tude of about 10,100 feet to 11,000 feet. It is most clearly shown at 
about 10,550 feet, below the trail leading from C. H. C. Hill to the 
Uncle Ned saddle in the ridge from Telescope Mountain, and on the 
north slope of the little spur indicated by the 10,650-foot and 10,700- 
foot contours on the map. The direction of the crevice is here nearly 
east- west, curving to the southeast in the upper part of its course. 

Where most distinct this fissure occurs on a northerly slope which 
is quite thickly wooded, and it would scarcely be noticed except that 
several trees on its line have been split from the roots up to 2 or 3 feet 
above the ground, in the manner shown in PI. XVIII, from a photo- 
graph taken by Mr. Tower. A stump of one tree cut off at about 2 feet 



1-10 GEOLOGY OF THE KIOO MOUNTAINS, COLORADO. 

above the ground has been split open since the tree was felled and the 
parts are now seen alx>ut 5 feet apart. According to Mr. J. O. Camp- 
bell, the tree was cut about 1894. Earth has filled in between the 
halves of this stump and to some extent under the split trees, indicat- 
ing that the movement has been gradual. It probably began, how- 
ever, before the felling of the tree, the stump of which has been split, 
for the two parts show that the tree was once cracked on the line of 
subsequent splitting and that this crack had been partly healed by 
growth. 

The crevice may he followed for 200 or 300 feet below the split trees 
by a crack in the soil, seldom open for more than 2 or 3 inches in 
depth, although a horse's hoof will sink in for a foot or more. Above 
the trees the crevice was traced almost continuously across the trail 
and up to 11. oho feel in the southernmost of the two distinct ravines 
represented on the map. 

Where the trees are split the crevice is at the base of a steep north- 
erly slope, L0 to L'u feet above a little bench, and perhaps 50 feet above 
a marked ravine. Farther up the slope the crevice runs for some 
distance in the bottom of a shallow but distinct landslide trench. It 
Crosses the trail on the south edge of some distinct outcrops of shale and 
sandstone, which are much broken up. but have a general southeasterly 
dip. Still higher the crevice was traced into the curving ravine in the 
isolated area of upper Hermosa shales and sandstones represented on 
the map. \\ here it was lost. 

Magnitude of tlu landdicU action. N<> part of C. El. C. Mill, as 
already defined, is free from evidence of landslides, and most of the 
pies, in surface is made up of the debris of those slides, though much 

of it. or possibly all of it. has been rearranged by movements since the 
original falls. Bui the evidence of the mines and prospects demon- 
strates that rock in place occurs at or neai' the surface in many locali- 
ties. These workings also show that the formations, which must be 
considered as practically in place, are almost universally in a terribly 
shattered condition, and w hile ore bodies in or near st ratification planes 
have been traced for lone distances, minor dislocations are frequently 
met with, and in several place- abrupt breaks have been encountered 
beyond which the ore has not been again found. In the discussion of 
the fault structure it has been explained that several known faults have 
been followed to the borders of ('. II. ('. Hill, and others must be 
assumed as present somewhere beneath the mantle of debris, so that 
in the present condition of exploration it can not always be ascertained 
whether the breaks in ore bodies are due to faults or to the superficial 
fractures bounding landslide masses, some of which may be reopened 
fault fissures. 

The amount of fragmental material encountered in tunnels varies 
greatly in different parts of the hill. Thus the Mountain Spring tun- 



cross.] SLIDES BETWEEN BURNETT AND SULPHUR CREEKS. 141 

nel penetrates loose chaotic material for 440 feet before a semblance of 
rock in place is found.. Much slide rock was found in the C. H. C. 
tunnel, and then it passed into greatly crushed beds, through which 
the structure can, however, be traced. In the Princeton tunnel much 
detrital material was passed through before rock in place was encoun- 
tered. 

In contrast to the tunnels just mentioned, the Pigeon and other mines 
in the northern part of the hill are almost wholly in rocks which are 
practically in place, though much fractured and disturbed. 

The principal trench seen in PI. XV is on the line of what is called 
the " big fissure " among those who have worked in the Pigeon, the 
Logan, and other connected claims. This is a zone of intense crushing 
of vein and country rock material 50 feet wide in some places, and the 
question 'arises whether or not some of the old veins — also faults in 
some cases— have not been opened anew during the shocks of the land- 
slide fracturing. 

RIDGE BETWEEN BURNETT AND SULPHUR CREEKS. 

One of the largest landslide areas of the district is the broad ridge 
between Burnett and Sulphur creeks, extending from about 11,000 
feet on the crest of the ridge down to the Dolores River, some 2,400 
feet below. In its present condition this area affords few local- 
ities where landslide phenomena are clearly exhibited, but by com- 
parison with other areas the landslide evidence is still most convincing, 
and the ridge is of much interest as illustrating an advanced stage in 
the history of landslide areas, when the ordinary agencies of degrada- 
tion have nearly completed their work of effacing the scars caused by 
the successive slips, leaving little evidence in the smooth slopes of the 
confusion existing beneath. 

The upper limit of this area is a rather sharp line crossing the crest 
of the ridge almost north-south at about 11,000 feet. This line is a 
well-marked trench of varying depth which runs back of the knoll 
having an elevation of 11,000+ feet, passes on the north across the 
flat at 11,175 feet, where a minor ridge juts out into Sulphur Gulch, 
and which on the south becomes a ravine, indicated on the map. On 
other sides the landslide has no closely definable boundaries. 

The southwest slope of the ridge is smooth and rounded in features, 
entirely covered by grass or timber growth, and contrasts very mark- 
edly with the opposite side of Burnett Gulch, with its prominent cliffs 
of stratified rocks and porphyries. This contrast is striking as ex- 
pressed on the topographic map, but is far stronger on the ground. 
The examination of this southwest slope shows no outcrops of rock in 
place except at the end of the ridge and very near the bed of Burnett 
Creek, nor are there the usual broken ledges characteristic of land- 



142 GEOLOGY OF THE EICO MOUNTAINS, COLOEADO. 

slide blocks. Instead of this, the few exposures where the character 
of the underlying materials can be seen, and the scattered prospect 
tunnels, reveal detrital matter of the texture of ordinary wash or 
slide rock. No tunnel seen has penetrated to solid rock. 

The physiographic detail of this slope is, however, most suggestive 
of landslides, especially when seen from some point of view like Land- 
slip Mountain. There arc many projecting knolls and local benches, 
irregular transverse depression- belonging to no drainage system, and 
general lack of persistent drainage channels. Most of this detail is of 
too small a scale for representation on the map. 

On the northeast side of the ridge there is a steep wooded slope, 
upon which at several places there are very distinct trendies running 
horizontally or obliquely along the hillsides, with sharp, furrow-like 
ridges on the outer side. Sonic of these modify the general slope so 
abruptly as to indicate that they belong to quite recent slips. Out- 
crops of rock are rare and are always of much broken and dislocated 
material. 

On or Dear the crest of the ridge leading from Expectation Moun- 
tain are the most distinct evidences of landslides. For several hun- 
dred feet below the upper limit of the area the broad top of the ridge 
is characterized by rounded knolls with Hat or shallow depressions 
between them. More or Less distinct ledge outcrops of sandstone, 
-hale, or porphyry are common on these knolls, but the greatest 
irregularity of dip and strike is found, and the most prominent beds 
are dearly not continuous. The character of this part of the ridge is 
represented in PI. XIX. a view from one of the upper knolls looking 
down the ridge. The dips observed in the mounds and knolls shown 
in this view are quite abnormal in most cases, being steep angles 
either down the ridge or to the east. 

No geological boundaries can lie traced across this obscure area, and 
this is conclusive evidence that the debris of the smooth slopes is not 
ordinary slide or talus. From the known structure of adjacent areas 
it is plain that the massive limestones of the Carboniferous, the Mon- 
telores porphyry sheet, and the grits of the lower llerniosa must 
underlie this mantle of loose material. From observations of Mr. 
Spencer the Rico formation may lie normally in place near the L0,600- 
foot contour, on the crest of the ridge. 

As to the end <>f the ridge, near the river, the evidence is not con- 
clusive as to how large a part of the sedimentary rock seen on the 
steep slope below the flat bench on the Burnett trail is in place and 
how much is landslide material. The outcrops near the bench level 
are of somewhat crushed and dislocated red or greenish strata, dipping 
westward as a rule. The red beds seem to belong at a much higher 
horizon than anyone which can normally occur here. The lack of expo- 
sures for such a distance above this bench renders a verdict as to the 



cross] SLIDES ON LANDSLIP AND DOLORES MOUNTAINS. 143 

origin of the red strata uncertain. Down near the river in fragmental 
material are the .sulphur deposits elsewhere described, and on the 
bank of the river several prospects show apparent roek in place 

LANDSLIP MOUNTAIN. 

One of the most perfectly exposed minor landslides of the Rico 
Mountains has taken place on the southwest face of a mountain on 
the divide south of Burnett Creek, for which the name Landslip 
Mountain is proposed. This summit presents to the north cliff faces 
of red Hermosa beds containing several intrusive porphyry sheets 
and dikes. The summit itself has a porphyry cap, and other small 
bodies occur on the ridge to the west. 

From the summit of Landslip Mountain to the saddle on the west, 
some 300 feet lower, and from this line southward nearly to the 
bed of the north fork of Wild Cat Creek, the surface is covered by 
landslide debris. None is found on the north side of the divide. In 
PI. XX may be seen the nature of the extreme upper part of this 
slide. The light-colored rock is largely porplryry, but there is also 
much red sandstone and shale, causing darker shades here and there. 

It is plain that the larger part of the porphyry belongs to the cap- 
ping sheet of the mountain, but lower sheets undoubtedly appear. 
The occurrence of the porphyry in sheet form in the sedimentary 
section is visible in many places, but accurate correlation of the shat- 
tered and disconnected exposures is impossible. The talus from the 
disintegrating slide blocks streams down the slope, but slide blocks of 
considerable size occur at intervals far down in the timber. The map 
shows some sinks and knolls below the part seen in PI. XX, and the 
phenomena of trench and knoll are repeated as far down as the rep- 
resentation of the map. 

DOLORES MOUNTAIN AND NEWMAN HILL. 

Landslide phenomena comparable with those that have been described 
are of very limited extent on Dolores Mountain, and are found only 
on the southern and western slopes. Nearly the whole southern slope 
is smooth and has a veneer of ordinary wash and talus, through which 
small outcrops project here and there. A landslide which is of recent 
date, since it sharply modifies the rounded form of a grassy slope, has 
taken place on the small ridge between the two southwesterly ravines 
indicated by the map. 

Above the slide bench, which is shown on the map by a bowing out 
of the 11,050-foot contour, the ridge has in general a very rounded 
outline, but near the bench is sharply sliced off by a plane having a 
strike N. 57° W. and dipping m SW. This plane extends to the 
bench and seems to represent the surface upon which sliding took 



144 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

place. While there are no distinct rock outcrops above or near the 
bench, the outer face of the little shoulder below it presents much 
broken-up strata, in part at least of the Rico formation, in masses 
several yards in diameter and of discordant dip and strike in different 
exposures. Small transverse trenches and fissures show that this mass 
is disintegrating, and a train of debris from it leads in fact far down 
the slope below. 

The physiographic relation of Newman Hill to Dolores Mountain is 
in some respects similar to that of C. H. C. Hill to Telescope Mountain, 
and the surface of Newman Hill is almost entirely of fragmental 
material. But it does not appear that landslides have played so 
important a role in producing this physiography as is the case on 
C. H. C. Hill. Yet the landslide's of the western and southwestern 
slopes of Dolores Mountain must have sent their debris in avalanches 
down upon the lower slopes, and unmistakable evidence of such 
materials air seen in a knoll at 9,850 feet northeast of the old - Enter- 
prise tunnel, and in several patches of coarse debris along the upper 
part of the hill, especially on the slope to Deadwood Gulch. 

REGION SOUTH OF BLACKHAWK PEAK. 

The ridge leading east of south from Blackhawk Peak, just within 
the bounds of the special map, exhibits landslide phenomena which 
belong to the early stages of the movement. From the porphyry 
capping of the knoll near Blackhawk Peak southward to the porphyry 
hill having an elevation of Ll,650+ feet, the rocks of the surface of 
this ridge are shattered and several blocks on each side have become 
detached and have slipped en masse or in avalanche down the slopes. 

Several of the principal fractures on which slipping has occurred 
are now represented by trench ravines, the most distinct one being 
that shown by the map on the east side of the main ridge. Porphyry 
slide forms the crest east of this ravine from the level of 11,800 feet 
up to the hill above, while the ridge to the west is composed chiefly of 
much broken-up sedimentary rocks. Another line of fracture runs 
nearly north and south through the depression on the flat top of the 
ridge north of the porphyry mass at 11,650+ feet. This break is 
evidently back of a mass which has started to slip down the eastern 
slope into the basin beyond the map line. 

From an elevation of 11,650 up to 11,900 feet on the broader part 
of the ridge under discussion the surface gives many indications that 
irregular blocks have begun to slip on each side of the ridge. There 
are several trenches crossing the ridge diagonally, some northeast- 
southwest and others northwest-southeast. Probably the notable 
amount of talus below the porphyry cliffs on the west has been caused 
by the fall and disintegration of one or more of the outer sections of 



DISTRIBUTION OF LANDSLIDES. 145 

the ridge. It is possible to map the porphyry sheet of this ridge in the 
general way expressed by the map, but broken-up portions of sedi- 
mentary beds are locally found along some of these cross trenches, 
which are supposed to belong to the strata normally above the sheet, 
but which may be due to marked irregularities in the upper surface of 
the porphyry, foi several sheets of this region are known to have very 
uneven upper surfaces. 

On the flat bench at the top of the porphyry are some open crevices, 
one notable one 3 or 4 feet wide, choked up by loose fragments to 
within a few feet of the surface. This seems to represent lateral dis- 
placement, doubtless on a layer of shaly sediments at or near the base 
of the intrusive porphyry sheet. 

On both sides of the head of Aspen Creek, and in the gulch east of 
the ridge above described, are many masses of debris with sharp 
boundaries, which originated in landslides or more common avalanches 
from certain places in the cliff's above. Some of these masses form 
knolls or benches, grassed over or timber covered, and may represent 
landslide blocks. 

DISCUSSION OF LANDSLIDE PHENOMENA. 

Pi.sfribution of the landsldes. — The landslides of special importance 
descnbed in the foregoing pages are all located within a circular or 
oval area 4 or 5 miles in diameter, the center of which is close to the 
town of Rico. This area is geologically in the heart of the Rico 
uplift or dome, as now dissected by erosion, and this fact seems to 
have much significance. Landslides of minor importance have taken 
place within the Rico quadrangle beyond the center indicated, but 
they are hardly more frequent than in many districts of this part of 
Colorado and are not so closely connected with the phenomena of the 
Rico Mountains as to be of any value in a discussion of the latter. 

While much the larger part of the surface within a circle 4 miles 
in diameter, with Rico at its center, exhibits distinct evidence of land- 
slide action, there are areas which are notable exceptions to this rule. 
The most striking are the ridge ending in Sandstone Mountain and the. 
northern part of Dolores Mountain. The bold cliffs of Sandstone 
Mountain are situated directly between the slide areas of Horse Gulch 
and C. H. C. Hill, and the rugged projecting ridges of Dolores Moun- 
tain might reasonably be expected to furnish large blocks under any 
general force exerted in this area. 

As an examination of the map will show, the landslide areas bear 
no definite relation to the distribution of rock formations in the dis- 
trict. On the contrary, in respect to neither sedimentary horizons 
nor eruptive masses does there appear to be any significant limitation 
of the landslides. 

21 geol, pt 2 10 



146 GEOLOGY OF THE RICO MOUNTAINS, COLOEADO. 

Character of the landslides. — On reviewing the characteristics of 
the Rico landslides it appears that the landslide action has been very 
superficial. This fact appears most strikingly by comparing these 
slides with those of the Telluride quadrangle. 1 adjoining the Rico on 
the northeast. About Rico slide blocks 100 yards in diameter, within 
which the formations bear their normal relation to one another, are 
decidedly rare, while at the west base of the San Juan Mountains one 
such block extends for 2 or 3 miles. All the landslide areas about Rico 
are plainly made up of a number of small separate .slips which were 
probably not contemporaneous. It is supposed that the slide block at 
the Puzzle mine is representative of those which cover the whole north 
slope of Darling Ridge. Some of the blocks may be larger than that 
at the Puzzle, but the latter illustrates the superficial extent of the 
blocks covering the slope above. 

The statement that the landslide phenomena are superficial applies 
strictly only to the masses which have slipped out of place by gravi- 
tation. Doubtless many of the fractures of the rocks which permit 
the detachment of blocks extend downward far beyond the limits of 
the slipping masses, but only the outer shell of shattered rock can 
move under the force of gravity. 

Aside from the fact of observation that the slide blocks are all small, 
the condition of the formations below the slide-covered surfaces affords 
further evidence 1 of the superficial character of the phenomena. The 
most striking case in point is that of C. 11. C. Hill. The topographic 
details of this hill, as illustrated in Pis. XV and XVI. indicate land- 
slip action over almost its entire surface, yet the ore deposits, both in 
vertical veins and in replacement masses, have been traced for con- 
siderable distances through shattered formations. 

Relations to topography. From the details regarding the various 
slide areas which have already been given, and from the illustrations 
of the plates, it is evident that the physiography of the Rico Moun- 
tains had acquired almost the detail it now exhibits when the landslides 
under discussion began. The only considerable modification of that 
physiography in the intervening time to the present has come directly 
from the landslides or indirectly through the rapid breaking down of 
the principal slide areas. The valley of the Dolores at the foot of C. 
H. C. Hill must have been of the exact type now seen above Burns. 
The stream bed of Horse Creek has plainly been interrupted by the 
Puzzle mine slide. 

The primary condition for a landslide may be generally stated as a 
thoroughl}' fractured state of the rocks on slopes, permitting the force 
of gravity to cause the fall; and were all the rocks of a mountain dis- 
trict to be uniformly shattered the mountains of most precipitous and 

i Geologic Atlas U. S., folic, 57, Tellurjde, Colorado, 1899. 



AGE OF THE LANDSLIDES. 147 

Irregular form would naturally experience the most extensive landslide 
action. Hut in the Rico district some of the most rugged mountains 
have undergone no visible degradation by landslips, even in the heart 
of the area most affected. Sandstone Mountain is the most striking 
instance of this immunity 

In harmony with this negative evidence is the positive fact that the 
ridges most thoroughly affected by the phenomena must have had 
comparatively gentle slopes at the beginning of the landslide epoch, 
due allowance being made for the obliteration of their boldest detail 
by subsequent events. 

Relations to <>f/nr Pleistocent phenomena. — The ordinary processes 
of degradation operative in the high mountain regions of Colorado 
have of course been active in the Rico Mountains during the long 
epoch of landslide action, and it scarcely need he pointed out that all 
the destructive agencies must have been especially effective within the 
landslide areas. The shattered landslip blocks themselves have been 
in high degree vulnerable to the attacks of solvent waters, frost, etc., 
and have in many cases rapidly disintegrated. The whole slope of 
Darling Ridge, as of other landslide areas, is practically without sur- 
face drainage channels, so permeable is the mass beneath to the rain 
that falls upon it and to the snow water. 

One effect of this saturation by circulating water has been to keep 
the fracture lines of attrition matter and many layers of crushed 
sandy shale in a soft condition, favorable to the slipping of more or 
less extensive masses whenever the support is weakened sufficiently. 
Secondary slides of this sort must have been frequent ever since the 
original shattering of the formations, and they are still taking place. 

The more exposed and isolated landslide 1 docks, if prevented from 
further slipping en masse, break up gradually, and a talus slope or an 
avalanche track often denotes the course of the more rapid disintegra- 
tion The destruction of the blocks on the south slope of Landslip 
Mountain is clearly illustrated by PI. XX, and the result of long- 
continued action in an area of extensive fracturing may be seen in the 
ridge extending from Expectation Mountain shown in PI. XIX. 

Age of the landslicU 8. —The epoch of the Rico landslides extends from 
their beginning to the present day. From the great number of the 
slides in this limited region it must be assumed that they are due to 
some very unusual force shattering the rocks to a remarkable degree, 
and it is most natural to assume, further, that that force was cata- 
strophic and principally exerted at one time — the beginning of the 
landslide epoch. It is therefore of prime interest to ascertain when 
these slides began. 

The evidence afforded by the relation of the slides to the topography 
of thedistrict has been given. The principal changes in the topography 
since the landslides began have been caused by the slides themselves. 
There has been practically no erosion in the Dolores Valley or in the 



148 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

more evenly graded reachesof its local tributaries in the landslide epoch. 

Of all the phenomena of Pleistocene age in this region there is none 
affording definite proof as to the remoteness of the time at which the 
fracturing of the formations took place. All the distinct alluvial for- 
mations, as flood plains, and the fans or aprons at the mouths of streams 
tributary to the Dolores, are referable to activities during the land- 
slide epoch. Even the glacial deposits seem to afford little evidence as 
to the age of the first landslides. The main traces of glacial deposits 
are in the eastern portion of the Rico Mountains and at places where 
landslides have not occurred. And the gravel deposits, which seem to 
be of glacial origin, have in most cases been more or less rearranged, so 
that little weight can be given to conclusions drawn from their present 
position. The landslide period was apparently contemporaneous with 
the glaciation. or nearly SO. 

The slides are definitely earlier than the forests growing upon many 
of them, and these growths are comparable t<> I he common forest 
growth of the high mountain areas of the State. 

Relation tofavlts. As the landslides occur in the heart of the Rico 
uplift they are coextensive in a general way with the principal fault- 
ing in the locks of the dome, and one of the most obvious hypotheses 
as to the origin of tin' landslides is based upon the assumption that the 
two phenomena are genetically connected. On analysis of the observed 
facts it appears that several of the principal landslide areas are trav- 
ersed by important faults, but that, on the other hand, some of the 
most C ple\ fault zones or tracts do not exhibit landslide action. 

The faults of C II. C. Hill seem at first glance to be parallel with 
the trenches of the principal landslides, running northwest -southeast. 
The strong fault veins of the we-t side of the Dolores, below Margue- 
rite Gulch, are in line with several crossing the ridge leading from 
Telescope Mountain to Nigger Baby Hill, and through the shattered 
intermediate ground of C. H. C. Hill run a number of veins in the 
same general course. These are invariably greatly broken up. so that 
they are now zones of loose fragmental material, as strikingly shown 
by the "big fissure," the quartz vein exploited in the Pigeon. Logan, 
and other claims, which lies below the strong trench of the view in PI. 
XV. As has been pointed out, the northeast cliff bounding C. II. ('. 
Hill seems to be parallel to a system of fault veins known in that area, 
and the landslides adjacent to the cliffs appear to represent great bands 
of rock between some of the fissures of that system. 

The cross faults, of which three are shown on the map, may have 
had some influence in subdividing the zones of the main system. 

The ridge from Expectation Mountain to the mouth of Burnett 
Gulch is probably traversed by the Deadwood and Spruce Gulch 
faidts. but their presence has not been determined, nor has any other 
fault been proved to exist in that area. 

It is not unlikely that several faults cross the Dolores from the east 



CROSS.] ORIGIN OF THE LANDSLIDES. 149 

into the landslide area of Horse Gulch and Darling Ridge, yet do indi- 
cations connect these fault courses with fracturing of the landslide 
period. The same is true of the north side of Horse (reek. 

The small landslide area on the ridge south of Blackhawk Peak is in 
the line of the Blackhawk fault, and some of the trenches have the 
general course of that fault, but as the actual dislocations of the fault 
have not been traced as far as the slide, it is not possible to show any 
dependent relation between those fractures of the rocks. 

As will appear in the discussion of Newman Hill, there is a great 
deal of recent Assuring and movement clearly proved in the mine 
developments, but the connection between that movement and the 
landslide of adjacent areas is a matter of inference. From the recent 
age of the landslides it becomes plain that if there is any causal con- 
nection between them and the older faults of the district it comes 
through lines of weakness in the rocks along those faults, of which the 
much later forces made use. The question is further discussed under 
the next heading. 

Origin of the landslide*. — The immediate cause of the Rico land- 
slides is manifestly the very unusually shattered condition of the rock 
formations on steep slopes, and the discussion of origin must be 
directed to the seat and nature of the force to which the intense shat- 
tering is due. The evidence concerning this force contained in the 
observations which have been recorded may be summarized as fol- 
lows: 

1. The principal landslides are confined to a small circular area in the 
heart of the Rico uplift, but do not cover all of that area. 

2. The slides are more recent than the topographic details of the 
mountains and valleys, excepting only some recent and minor features. 

3. The shattering of the rocks varies locally in degree. 

•i. The shattering is independent of lithological character and struc- 
tural attitude of the formation, and there is nothing in either of these 
conditions especially favorable to landslides. 

5. The principal landslide slopes are in the courses of many known 
faults, but several intensely faulted areas of rugged topography do 
not exhibit landslides. 

(5. Many fault veins seem to have been opened again by the shock 
producing the shattering of the formations. 

7. The shattering extends below the surface zone of actual sliding, 
and to unknown depths. 

The consideration of all observed facts leads to the comprehensive 
statement that in geologically very recent time a part of the central 
portion of the Rico Mountains suffered a severe shock, shattering the 
rocks at the surface and to unknown depths. As a result of this shat- 
tering many landslides have occurred where other conditions were 
favorable. This shock must have had its source in greater or less 
depth, and may lie referred to as an earthquake shock. 



150 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

Two important sources of earthquake shock arc specially recognized, 
viz, that originating in the relief of tension arising from structural 
movements of the earth's crust, and that connected with volcanic phe- 
nomena. The Rico Mountains represent a center of upheaval and 
intense faulting, and of igneous intrusions of a nature not strictly 
volcanic. It seems natural to suppose that seismic disturbances must 
have taken place at the surface of the Rico dome during the periods 
of faulting and during the intrusion at least of the monzonite magma 
in the channels represented by the stocks of to-day. But those dis- 
turbances took place at so distant an epoch that the connection of the 
shocks now under discussion with either of them is not plausible. 

A hypothesis to explain the earthquake shock of recent time in the 
Rico Mountains must satisfy a number of conditions of observation, 
and the most difficult facts to meet seem those found to hold true in 
regard to the Darling Ridge locality. Here is a considerable area con- 
taining nearly horizontal rock formations, penetrated by sheets and 
one or more stocks of monzonite. The topography is not specially 
rugged, faulting is certainly much subordinate in extent to that of 
adjacent areas like Silver Gulch, yet the most profound and complete 
fracturing seems to have occurred in this area. 

It is a matter of common belief to-day among structural geologists 
that movement is still in progress on many old fault lines which con- 
tinue to be lines of weakness. The recent movement is thought to be 
gradual, ami if thi' existing tension finds sudden relief by dislocation, 
even of minor extent, it is supposed that perceptible or even violent 
earthquake shock may be experienced at the surface. These ideas 
have been applied notably to the explanation of the great Charleston 
earthquake of L886. 

If, now. the recent -battering of the rocks in the Rico district be 
assumed to be the result of faulting, an adjustment of the rocks under 
Stresses still existing at this center of uplift, the opening of old faults 
may be explained, and the great shattering on new and irregular frac- 
tures may be regarded as a natural distribution of the shock in the 
superficial zone, where resistance to fracture is less" than in depth. 
But while little positive evidence appears to oppose this hypothesis, 
it must be considered remarkable that Silver Gulch, the locality of 
most intense and deep-seated faulting, judging from surface disloca- 
tion, has not been the scene of landslides. On the other hand, the 
locality where the shattering force seems to have vented itself in great- 
est violence is certainly not one of the principal fault areas of the 
region, although some faulting is to be considered probable. 

The hypothesis that the supposed Rico earthquake originated in 
volcanic forces seems to the writer to be better adapted to the require- 
ments of the case than that of recent faulting. The ultimate cause of 
volcanic earthquake shock need not be discussed here, for it is one of 
the most commonly recognized facts of observation that such phenom- 



cross.] ORIGIN OF THE LANDSLIDES. . 151 

ena are characteristic of volcanic regions. Rico lies almost immedi- 
ately adjacent to the San Juan volcanic area, one of the most exten- 
sive in the United States, and it is certainly reasonable to assume that 
of the earthquakes doubtless experienced in this region some were 
especially felt about Rico, even if there was nothing in the conditions 
beneath the Rico uplift to produce local shocks at that center of 
igneous activity. Given a violent disturbance of volcanic origin be- 
neath the Rico dome, it may be assumed that its transmission to the 
surface would be influenced by lines of weakness, such as existing 
faults, and coexistent earth stresses might determine which fissures 
out of a complicated system would be most affected. Under this 
hypothesis the reopening of fault veins is a result and not the cause 
of the shock by which many other new fractures were made in the 
rocks. 

The volcanic hypothesis seems to furnish an explanation of the intense 
fracturing of the rocks on Darling Ridge. It is conceivable that the 
monzonite stock, penetrating the heterogeneous series of sedimentary 
rocks as a massive and continuous body extending far toward the sup- 
posed local seat of volcanic energy, would serve to transmit to the 
surface in relatively undiminished force the shock assumed b} r this 
hypothesis. It is certainly true that the impression as to the violence 
of the force which has been here exerted has been far stronger on the 
writer's mind when among the huge blocks of monzonite on the summit 
of Darling Ridge, and well within the borders of the stock, than when 
at any other locality in the Rico Mountains. 

The gigantic landslides of the Telluride quadrangle have also been 
ascribed by the writer to earthquake shock. 1 But there is so great a 
difference between these slides and those of the Rico Mountains that 
different causes might well be assigned. The Telluride landslides are 
enormous. The rocks affected are mainly a great volcanic series resting 
on soft Cretaceous shales — a lithological element of much importance 
lacking in the Rico Mountains — and they have occurred upon the bold 
front of the San Juan Mountains. Faulting is there very subordinate 
in importance, and that the dislocation of these huge masses should be 
referred to earthquake shock of volcanic origin is natural under the 
circumstances. The relation of the Telluride phenomena to those of 
Rico is significant mainly in that they have occurred in the same gen- 
eral period of recent time; it is but 1-t miles from Rico to the great 
landslide area adjacent to Trout Lake, and if the landsl des of the 
Telluride quadrangle were due to volcanic shock it seems inevitable 
that that disturbance must have been strongly felt in Rico. It is a 
possibility that the fractures of the rocks in the two localities leading 
to landslides were primarily due to the same great disturbance, trans- 
mitted to the surface in the Rico district under local conditions already 
discussed. 

'Telluride folio 



CHAPTER VI. 

EROSION OF THE RICO DOME AXD RECENT GEOEOGIC 
HISTORY. 



Bv Arthur Coe Spencer. 



EROSION OF THE DOME. 

General statt ment. — Of all the events of Tertiary time up to the in- 
trusion of the igneous masses and the uplift of the dome we have no 
record in the phenomena presented at Rico. In the adjacent country 
to the north and east, however, we have evidence that the Mesozoic 
was followed by extensive erosion which was continued for a sufficient 
length of time for tin 1 removal of the entire sedimentary section from 
the central portion of the San Juan region. We have also in the San 
Miguel formation the evidence of the existence of a large lake in the 
later part of this period of erosion, and in the breccias of the overlying 
San Juan formation a witness to the beginning of volcanic deposition, 
which was continued until the region was covered to a deptli of several 
thousand feet with pyroclastic and massive extruded rocks. Doubt- 
less, as pointed out in the Telluride folio. 1 this upbuilding was accom- 
panied by vigorous erosion, but until the cessation of the former the 
latter was probably in abeyance. Now. the early Tertiary history at 
Rico must have been that of the San Juan at large, but the amount of 
post-Mesozoic erosion is not known, nor is the probable thickness of 
the volcanic accumulations which covered the site of the present moun- 
tains to be estimated; but here they were doubtless undergoing erosion 
during deposition, and upon the land surface formed by them the 
drainage system was being developed from which the present streams 
have inherited many of their main features. 

At the inception of the Rico dome the extruded rocks which covered 
the San Juan country were being attacked upon all sides by streams 
whose positions were probably determined by the distribution of the 
volcanic materials. So long as eruption continued the stream courses 
were constantly liable to alteration by lava flows, but with the cessation 
of volcanic activity each stream would maintain the course it then held, 

1 Geologic Atlas I'. S., folio 57, Telluride, Colo., 1899, p. 1, Tertiary history. 
152 



bpenceb.] EROSION OF THE RICO DOME. 153 

deepening its channel and sapping at its head to extend its canyon into 
the central mountainous region. Jt seems probable that the Dolores 
River had assumed its present course previous to the formation of the 
Rico dome, since, supposing that the surface at the time the dome was 
formed was sufficiently smooth for the development of consequent 
drainage upon its slopes, it is difficult to understand how one of the 
radial streams thus resulting could have gained so distinct an advantage 
over the others that it would finally cause their complete diversion. 
This objection is particularly applicable at Rico, because the relations 
of hard and soft rocks in the region to the north of the dome are such 
that diversion of the present headwaters of the eastern branch of the 
Dolores must have been accomplished by the western branch of that 
river long before any stream originating on the southern slope of the 
Rico dome could have extended its course northward across the oppos- 
ing strata on the north side of the dome structure. 

As stated in a preceding chapter, it is believed that the Rico defor- 
mation accompanied a general regional uplift. If this idea is correct 
it follows that while erosion has been continuous in the central San ,1 uan 
since the beginning of volcanic deposition an epoch of increased activity 
in erosion must have followed this elevation, even if the streams had 
previously found permanent courses. 

The actual amount of erosion since the Rico uplift can not be esti- 
mated, since its effects arc not separable from those of the epoch pre- 
ceding. It may be surmised, however, that the volcanic rocks had 
not been removed entirely and that sediments above those now exposed 
may have been present at least well up into the Mancos shale at the 
time of uplift. 

The epoch of erosion since the latest important uplift of which we 
have any record in the Rico region may be divided into three stages. 
which are applicable to the San Juan at large as well as at Rico. During 
the first stage the greater amount of erosion was accomplished and the 
topography had reached practically its present form. During the 
second there was an accumulation of ice with the formation of local 
glaciers and the production of such forms of erosion as glacial circques 
and U-shaped valleys. To the same part of the epoch belong the land- 
slide phenomena, though their exact age relations are not to lie made 
out at Rico. In the Telluride region, however, there is some evidence 
for believing that the landslides had taken place before the maximum 
advance of the ice. The landslides are so important a feature of the 
geology of the Rico region that they have been made the subject of 
special study by Mr. Cross, who describes and discusses them in a sep- 
arate chapter. The third or present stage dates from the retreat of 
the ice, which is geologically very recent, as shown by the small 
amount of erosion that has been since accomplished. 

The correlation of the latest epoch of erosion with the accepted divi- 



154 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

sions of geological time is a question which can not be solved at Rico. 
If the age of the local uplift be accepted as Tertiary, the first stage 
must be considered as also belonging to that period, in part, at least. 
If, on the other hand, the uplift could be considered as closing the Ter- 
tiary, all subsequent events would belong to the Pleistocene. In favor 
of the former conclusion we have the ore-bearing veins, the deposition 
of which must have required a long time, but which are manifestly later 
than the deformation. 

Prr-dhicnil erosion. — It has been shown that erosion in the Rico 
region has probably been continuous since early Tertiary time, and 
that there is no way of determining the relative amount of degrada- 
tion in the earlier and later epochs of the period, or of separating the 
latest Tertiary erosion from that of Pleistocene time. Whether the 
Dolores was flowing in a shallow valley or a deep canyon previous to 
the domal uplift at Rico can not be surmised, but before the com- 
pletion of the structure the stream had doubtless cut a deep trench 
well down toward the base of the volcanic rocks which are supposed 
to have covered the region, and possibly into the Mesozoic sedimen- 
tary rocks, upon which they probably rested. This erosion belonged 
to the epoch of deformation. It was succeeded by continued erosion 
of the present epoch as arbitrarily limited by the completion of the 
distinct uplift. Al lhi> early stage of erosion the adjacent streams 
must have had practically their present positions, though possibly 
they have since enlarged their headwater drainage on the Hanks of the 
Rico Mountains at the expense of the neighboring tributaries of the 
Dolores. This would naturally follow from the interior streams 
having to encounter rock more difficult of corrasion than the outside 
streams, and seems to be indicated by the greater length of the exterior 
tributaries. 

With the downward cutting, which has since continued, there has 
doubtless been concomitant elevation, but of this there is no evidence 
in the immediate vicinity of Rico, though within the Rico quadrangle, 
some 10 miles or so to the south, there are gravel beds about 4ou feet 
above the present valley floor, showing the former position of the 
stream bed and indicating an uplift since their deposition. The effect 
of erosion within the mountains lias been as though the river had cut 
its way at once to the present position and then side streams and 
gullies had completed the grading of the slopes. It is believed, 
however, that several distinct uplifts have occurred, but the pauses 
between them left no records because of the fact that the liver was 
cutting its channel and not at any time widening its valley, so that the 
valley was successively deepened, and under conditions of heavy pre- 
cipitation the slopes of the valley walls were gradually reduced with ■ 
out the production of terraces. 

The topography is always in close sympathy with the geolog}', and 



spencer.] PRE-GLACIAL EROSION. 155 

almost every feature of the landscape not directly referable to the 
phenomena of the landslides is the result of differential erosion. The 
softer rocks have been carved away, leaving- the more indurate as 
cliffs or steep slopes between more gentle acclivities and determining 
the positions of the main mountain masses. The rocks which have 
been sufficiently massive to form mountain caps are mostly intruded 
porphyries, though the La Plata sandstone always rises as a knob above 
the general level of the adjacent ridges. Of the few high peaks capped 
by other sediments than La Plata, Telescope, and Sandstone mountains 
are the only ones not protected by a very massive sheet of porphyry 
lying within 100 to 200 feet of the top. The former is capped by a 
heavy conglomerate of the Dolores and is not entirely without pro- 
tecting porphyries in its upper part, but the latter is composed of the 
Dolores sandstones entirely, though it is in reality a ridge leading to the 
much higher Elliott Peak, which is doubly protected from erosion by 
the La Plata sandstone and an overlying porphyry mass, so that the 
preservation of Sandstone Mountain may be considered as incident 
to the presence of the more prominent peak. 

The monzonite stock upon the west side of the river has been suffi- 
ciently resistant to form a ridge both south of Aztec Gulch and in the 
main divide south of Horse Gulch, though in neither place does it 
reach to as high an elevation as the porphyries of the adjacent peaks. 

The distribution of the laccolithic porphyry masses in the sediments 
has been discussed in a previous chapter. Their presence in the upper 
part of the Dolores formation has determined the zonal grouping of 
the principal mountain peaks about the center of the dome structure. 
In fact, it is to these porphyries that the Rico Mountains owe their 
existence. Had they not been encountered by the streams, the latter, 
in dissecting, would have given to the dome a molding scarcely differ- 
ent from that which they have impressed upon the adjacent areas of 
sedimentary rocks; the concentric outcrops of the harder beds would 
be expressed in knolls or curving ridges, but the general elevation 
would have been much less than at present. 

The positions of the side streams of the mountains have probabty 
persisted from a very early date, and they are in no way dependent 
upon the distribution of the rocks that they now cut across, though 
the}' may have been located by the occurrence of porphyry masses in 
the central part of the area at horizons which have now suffered com- 
plete erosion. Both the main stream and its tributaries had reached 
practically their present position before the change in climatic condi- 
tions tilled the upper valleys with ice. The dissection of the uplifted 
rocks was almost as complete as at present; the entire sedimentary sec- 
tion and its accompanying intrusions had been cut through and the 
Algonkian rocks had been exposed. Measured by its geological effects, 
the time which has subsequently elapsed is relatively very short; land- 



156 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

slides have locally modified the surface; the ice streams remolded the 
valleys slightly, scouring and depositing; flood waters in the main valley 
deposited gravel terraces, which have since been largely removed. But 
all of this is very unimportant in comparison with the great erosion 
subsequent to deformation and previous to glaciation. 

GLACIATION OF THE RICO MOUNTAINS. 

Forms oft videna .- -Evidence of the former existence of local gla- 
ciers in the Rico Mountains was to be expected from a knowledge that 
the higher portions of the San Juan region had been at one time prac- 
tically covered by an ice sheet. The facts leading to this conclusion 
have yet to be correlated before any general discussion can be 
attempted, but many of the topographic features illustrated on the 
maps of the Geological Survey are sufficient to indicate the former 
existence of glacial ice in the high mountainous region of the San Juan. 

The amphitheaters usually containing small lakelets, in which the val- 
leys have their heads, are to the student of glaciers and their work 
prima facie evidence of ire accumulation. Moreover, in the region 
there are many valleys with the U -shaped cross section; there are also 
morainal accumulations, scored and scratched rock surfaces, and even 
the characteristic form of glacial erosion known as roches moutonnees, 
all of which serve to prove the general fact of glaciation. 1 

At Rico the record of the ice invasion is seen in certain topographic 
forms, in lock scoring, and in accumulations of debris, but none of 
these are strikingly prominent or characteristic, from which ii seems 
that because of their somewhat lower altitude and their isolation the 
Rico Mountains were not so completely dominated by the ice as were 
the higher mountains adjacent. They formed a local center of 
accumulation, and though the greater number of the basins at Rico 
were probably piled high with snow there were only two or three 
cases in which the accumulation became sufficiently deep for the con- 
solidation of the snow into true glacial ice. 

Topographic < violence. — The topographic features of the Rico Moun- 
tains are disappointing as criteria for the determination whether or 
not a given gulch has supported an ice stream. Only a single basin 
of all those represented could lie definitely recognized as a glacial 
cirque from an inspection of the topographic map. This one, which 
lies just east of Allyn Gulch, is quite typical of the amphitheater as a 
glacial form, but is somewhat obscured by debris from the surround- 
ing walls. Three other somewhat cirque-like basins draining into 
Horse Gulch occur on the southern side of Sockrider Peak. Possibly 
the lack of characteristic form in some instances may be due to 

i On the glacial phenomena of this region see the Telluride folio and a paper by George H. Stone, 
entitled The Las Animas Glacier; Jour. Geol., Vol. 1, 1893, pp. 471-475. 



si-kmkk.] GLACIATION. 157 

accumulations of talus and .slide rock, but in the main it seems that 
amphitheaters have never been excavated even at the head of valleys 
otherwise known to have been tilled with ice. 

A second topographic feature which is often characteristic of 
glaciated areas is seen in the distributed drainage in the main head of 
Silver Creek, which lies within our area just to the east of Blackhawk 
Peak, whence the stream, after running northeastward for a short dis- 
tance, turns into its westerly course cast of the mapped area. Here 
there is a broad slope of porphyry from which the ice has swept most 
of the surface debris, and over this slope the waters flow in small con- 
verging but independent rivulets rather than in a single stream gath- 
ered into a central channel. 

The valley of Silver Creek is broader at the bottom than the ordinary 
gulch eroded by running water, and it is believed that the more open 
valley is to be explained by the former presence of an ice stream, 
since such a broadening of water-cut valleys is known to be usually 
characteristic of glacial action. Likewise in the case of Horse Gulch 
the same origin may be. suggested, though here it is evident that land- 
slides have entered into the development of the valle} r cross section, so 
that the glacial origin is involved in more doubt. In none of the other 
gulches is there suggestion of any erosion except that of running water. 

Evidence of glacial action, based upon scored rock surfaces, is meager. 
A few small surfaces of polished and striated rock were observed near 
the head of Bull Creek, west of Calico Peak. Small patches of 
smoothed and striated sandstone were noted about 300 feet above the 
river, just south of Marguerite Draw and near the bed of Deadwood 
Gulch, at an elevation of about 10,150 feet, Also limestone exposures 
just above the falls in Deadwood Gulch (elevation 9,800 feet) are planed 
and scored. Elsewhere no distinct markings have been observed, 
except in the head of Silver Creek, where the sloping floor of por- 
phyry shows some scoring and scratching besides the general cleaned- 
up effect due to the removal of surface debris through the action of 
moving ice and snow. The general absence of such features is not, 
however, to )>e wondered at, since the character of most of the rocks 
in the valley is not suited to the preservation of fresh surfaces. 

Glacial debris. — Passing now to the accumulations of glacial debris, 
it may be said that none of the deposits show the ordinary topographic 
forms of moraines or kindred features, but occur merely as gravels 
or loose rock fragments in such positions that they can hardly be 
accounted for as ordinary terrace gravels. The character of these 
deposits is, for the most part, typical of glacial materials which have 
not suffered long transportation. Angular or subangular fragments 
of the various rocks within the drainage of the former ice stream are 
thrown together in the utmost confusion, rounded pebbles being of 



158 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

unusual occurrence. In the mapping of the surface materials it has 
been found impossible to discriminate all the deposits according to 
their origin, so that the glacial gravels are not represented as distinct, 
and, indeed, the different forms of loose debris intergrade in such a way 
that they are often indistinguishable on the ground. Accumulations 
found along the south side of Newman Hill, next to Deadwood Gulch, 
have been attributed to an ice stream which occupied the upper part 
of the gulch. Those near the mouth of Allyn Gulch are to be attributed 
to a similar ice stream and were probably deposited at a time when the 
stream in Allyn Gulch did not join that of the main valley. The heavy 
gravels which occur in the northern part of Newman Hill contain 
much Waterworn material, which may have been deposited from a 
stream flowing along the south side of the Silver Creek glacier when 
it extended as faras the river, completely closing the channel of the 
tributary to the waters of Allyn Gulch. Doubtless avalanche mate- 
rial from the slopes of Dolores Peak has given rise to much of the 
covering of Newman Hill, and it is also certain that there have been 
landslides, but the presence of waterworn pebbles requires some such 
explanation as that given above. 

The rounded ridge which marks the entrance to the valley of Silver 
Creek may also be mentioned, since it has an external appearance simi- 
lar to kames or eskei'S, but it is really composed of sedimentary rocks 
and intrusive porphyry and is merely capped by gravels. It is conse- 
quently a remnant of erosion rather than a constructed form. 

In Papoose Gulch and on the eastern slope of Mount Elliott there 
are surtieial deposits which are related to the glacial deposits in origin, 
and are probably in pari of the same age. They consist of heterogene- 
ous masses of rock fragments of various size filling the gulch or form- 
ing a ridge, as in the last locality mentioned. These are supposed to 
have been formed by materials which have accumulated at the base or 
along the sides of great snow banks which tilled the basin above, but 
never attained the thickness requisite for the formation of true ice. 
Similar accumulations of recent origin are frequently seen in moun- 
tainous regions of heavy snowfall. They are often to be noted in the 
San Juan region, but these particular occurrences possibly date back 
to the time of the ice invasion. 

Coarse gravel beds, which from their position suggest a considera- 
ble former extent of such material-, were observed by Mr. Cross on 
the slope north of the monzonite arm that comes down almost to the 
houses in Piedmont. At an elevation of 9.500 feet, or about 700 feet 
above the river, an excavation in the wooded surface reveals a mass of 
very round bowlders lying in tine gravel. Among the rocks repre- 
sented were blue limestone, greenish sandstone, and vein quartz. The 
bowlders are very unlike the angular fragments which are sparingly 



spencer.] GLACIATION. 159 

scattered about on the surface. These angular blocks, often 3 feet or 
more in diameter, seem to have come from up the river, for red Dolores 
sandstone is common among them. Bowlder gravels have also been 
exposed in prospects near the line of the Calumet vein and about 300 
feet above the river. So much of the surface south of Aztec Gulch is 
timbered, with no solid rock outcrops, that it seems possible that there 
may be much of this gravel in the vicinity. 

On the slope below the tufa bench south of Sulphur Creek, at about 
300 feet above the river, there are several patches of coarse gravel 
beds. Among the fragments noticed here was one block, nearly 3 feet 
in diameter, of the peculiar hornblendic porphyry known only in dikes 
in the Algonkian schists above Rico. 

These two occurrences of heavy gravels indicate a much greater 
amount of probable glacial debris in the Dolores Valley than is to 
be inferred from am- other evidence observed. Knowlege of these 
gravels is clearly too meager to warrant generalizations upon them 
at present. 

Still another class of deposits which may be tentatively referred to 
the time of the ice invasion is seen in the gravel terrace upon which 
the town of Rico is partly built, and the similar and probably corre- 
sponding gravels which occur on the slight bench about 40 or 50 feet 
above the river bed upon the west side north of the mouth of Sulphur 
Creek. The gravels are best exposed in the cutting for the roadway 
to the railroad station, but are known to form the edge of the terrace 
for nearly half a mile toward the south. It seems probable that these 
gravels represent the level of the river valley at some particular period 
of glaciation. 

Collectively the phenomena cited in the foregoing paragraphs are 
believed to warrant the conclusion that true glacial streams at one 
time occupied the valle}- of Silver Creek and its tributaries and that 
of Deadwood Gulch, and that in the upper part of Horse Gulch there 
were important accumulations of ice; which maj^ or may not have 
reached into the lower part of the valley. Deposits of a morainal 
character not hitherto mentioned are known to occur beyond the lim- 
its of our map in the northern tributaries of Scotch Creek, and these 
indicate that there were short glaciers on the southeast side of the 
eastern part of the mountain group, but be} T ond this we have no fur- 
ther proof of individual ice streams in the Rico Mountains. Others 
may have existed, but their marks have been obliterated by surface 
materials of another origin or by the erosion which has taken place 
since their dissolution by climatic conditions. All the facts available 
point to the very local nature of the glaciation of the Rico Mountains 
and to the short duration of glacial conditions. 



160 GEOLOGY OF THE EICO MOUNTAINS, COLORADO. 

RECENT GEOLOGIC HISTORY. 

Many of the features of post-Glacial geology at Rico are inseparable 
in origin from similar features of Glacial and earlier time, since in 
those parts of the area that were not covered by the ice similar proc- 
esses of general erosion and of local deposition were active throughout 
the Glacial stage. For this reason, in classing the following phe- 
nomena as recent, there is no intention of limiting their age to the 
post-Glacial, but rather to indicate that the conditions which have pro- 
duced them have continued down to the present time. The recent 
phenomena of the Rico region may he classed as those of erosion and 
those of deposition. The latter will include landslides, talus and ava- 
lanche materials, river gravels, and spring deposits. 

Post-Glacial erosion.— It the gravels observed by Mr. Cross at an 
elevation of Too feet above the river on the northern edge of the 
monzonite are really of glacial origin, they indicate a much greater 
accumulation of such debris in the Dolores Valley than would l>e sug- 
gested by any other occurrences. Hut even it' they are glacial, the work 
of the river seems to have been largely the removal of the gravels, with 
little cutting into the underlying rock. In Deadwood and Allyn 
gulches the streams have cut down through the unconsolidated gravels 
of glacial origin, but this is a task which they could have easily 
accomplished in a short time. Similar indications of the small effect 
of post-Glacial bed-rock erosion are seen [n Silver Creek, where the 
stream has locally excavated narrow canyons in the wider valley of 
glacial origin, but these canyons have in no instance exposed the bed 
rock to a depth of more than possibly l'o feet, and in many places the 
stream is working upon debris of very recent origin, which has been 
thrown into its channel from the side gulches and ravines. All the 
evidence serves to point to the recency of the glacial occupation and 
to the small amount of erosion which has since ensued. The present 
topography is in no essential feature different from what it was pre- 
vious to the accumulation of the ice. Before thai the streams had 
found their present courses and had practically assumed their present 
grades. Greatly in excess of any topographic changes due to erosion 
are those attributable to the constructional features which are dis- 
cussed in the following paragraphs. 

Varieties of surf ac< deposits. — The surface deposits at Rico are of 
very diverse character and origin, and. as has been seen in the dis- 
cussion of the glacial gravels, they are not easily separable as to origin. 
They are very troublesome to the geologist, since they cover the cen- 
tral part of the region to such an extent that it has been found impos- 
sible to work out the geology of the solid rocks underlying. Conse- 
quently it is necessary to represent them on the map, and for this 
purpose live distinct patterns have been used to distinguish (1) areas 



.] RECENT GEOLOGIC HISTORY. Ifil 



made up principally of landslide material; (2) valley gravels; (3) allu- 
vial cones; (4) spring - deposits ; (5) materials of other origin, such aa 
avalanche, glacial, and surface wash. 

Lan<Mid<x. — The most important surface deposits in the Rico Moun- 
tain are of landslide origin. One such slide has materially altered the 
grade of the Dolores River north of Rico, others have changed the 
profile of Horse Gulch, while still others lend their characteristic 
pseudo-glacial topography to the mountain slopes in several places. 
This feature of the Rico region has been specially studied by Mr. 
( !ross, and its description and discussion are given a separate chapter 
in this report. 

Talus. — Accumulations from the wasting of cliffs are related in 
origin to landslides, hut are composed of many small blocks loosened 
by frost action or by heavy rains, whereas landslides, though they 
may eventually become very much broken, are at first essentially large 
masses. Talus forms are of frequent occurrence at Rico, and while 
in many cases, ("specially in the lower parts of the mountains, their 
even slopes are covered with vegetation, in other cases they are. 
entirely bare and then suggest the manner in which they were formed, 
namely, by the rolling and sliding of loose rock fragments under the 
action of gravity. They are well illustrated in several of the accom- 
panying plates, particularly in PI. VI (p. 28), showing the steep talus 
at the base of the Sandstone Mountain cliffs, and in the view of Calico 
Peak (PI. VII, p. 32) and that of Blackhawk and Dolores peaks from the 
north (PI. IV, p. 24), The long talus streams upon the west slope of 
Nigger Baby Hill are largely derived from the mines which are situated 
at their heads, but the whole adjacent slope is covered by natural talus 
or wash through which very few outcrops appeal'. 

Belated to talus are the materials dislodged by avalanches and 
deposited where their force is spent. Much of the loose material 
upon Newman and C. H. C. hills has been brought down in this way, and 
the paths which have been cut through the timber upon the western 
slope of Dolores Mountain may be made out from the photograph of 
this slope (PI. Ill, p. 22). Other ravines than these, which have been the 
tracks of snowslides, may be seen at various places. Some of the best 
marked are on the south side of Burnett Creek, upon the flank of 
Landslip Mountain. 

The deposits of Papoose Gulch and in the head of Marguerite Draw 
west of Mount Elliott have been mentioned in discussing the glacial 
phenomena, where they arc considered as connected with former great 
snow banks. Probably this is. in part at least, their true origin, but 
avalanches may have been also concerned in their formation. 

Surface wash. — In regions where the agents of erosion have been 
as active as at Rico rocks do not decay in situ by surface weathering, 
and consequently residual soils, such as cover tin' rocks in many low- 
l'1 geol, rr 2 li 



162 GEOLOGY OF THE RICO MOUNTAINS, COLORADO. 

lying- regions, do not accumulate. Surface wash is composed almost 
entirely of fragments derived from the higher slopes of the mountains, 
or from the disintegration of landslides which, gradually moving 
toward the valleys under such effective aids to gravity as snow, rain, 
and frost, have been spread in varying thickness over extensive slopes, 
hiding the underlying formations as completely as have the more 
massive surface deposits. As may be inferred from such an origin, 
the materials of the surface wash are as a rule more completely pul- 
verized than the other forms of surface deposits. 

As in the case of all the surface deposits, the representation of surface 
wash on the map is generalized and the indicated boundaries are to be 
taken as approximate. The symbol under which they are included is 
intended to apply to all areas not referable to the three classes of land- 
slides, valley deposits, and alluvial fans. It thus comprises the materi- 
als of mixed origin covering Newman Hill and the opposite slope west 
of the river. 

Valley deposits. — The valley deposits of the Rico region comprise 
the gravels of the present flood plain of the river. They consequently 
occur in a band across the area and bordering the river, but inter- 
rupted above I Corse < rlllcb by the great landslide at the base of ( '. H. ( '. 
Hill. This mass of rock which has been projected into the valley has 
pushed the stream against the western bank of the canyon, where it is 
now cutting in the -olid lock- of the lower llermosa. As may be seen 
by referring to the topographic ma]), it ha- interfered with the natural 
grade of the river, which is now abnormally steep adjacent to the slide 
block upon the lower side and as notably low in the reach upstream 
from it. The landslide at first formed a dam across the river, causing 
slack water for perhaps a mile and a half upstream. From the even 
spacing of the contours below the dam it is believed that the original 
stream bed at the lower end of the Burns meadow is approximately 
75 feet below the present position of the river, the same figure repre- 
senting the thickness of the material- deposited by the river at this 
place. If the same spacing which is noted below the landslide were 
continued upstream the 9,050-fool contour would have approximately 
its present position, so that it may be taken to represent about the 
upper limit of the effect of the landslide in changing the stream grade. 
From the dam to the present crossing of this contour the distance is 
slightly in excess of 1 mile, and the fall of the stream is not more 
than 25 feet, or less than one-fourth the normal fall for this distance. 
The northern edge of the landslide block and the flat above it are 
shown in PI. XVI (p. 142). 

The materials of the valley deposits are coarse gravels and sands 
which the river has derived from its tributaries and which it has rolled 
along and distributed within its immediate valley. 

AlluiyoJ fans. — ; The steeper gulches which open directly into the 



spencer.] RECENT GEOLOGIC HISTORY. 163 

Dolores Valley have all afforded detritus faster than the river has been 
able to carry it off, so that the debris brought down by the side streams 
has accumulated in conical banks at the mouths of the gulches. Such 
accumulations are commonly known as alluvial fans. They are a 
characteristic feature of the union of streams of steep grade with 
those of low declivity, since the transporting power of the steeper 
streams is suddenly diminished when their grade is reduced. The side 
streams at Rico do not at ordinary times carry any appreciable load of 
gravel, transportation being confined to times of flood. Heavy showers 
and cloud-bursts sweep debris into the steep gullies, and this, carried 
down to the main valley, is dropped, and the channel of the stream 
becomes inclosed by natural dikes, so that on becoming choked at any 
time the torrent will take a new course and, changing from time to 
time, will finally have swept through an arc limited b} r the valley 
walls and varying in width from 90 to 120 degrees. It is by thus 
changing its channel that the stream is able to build up the conical 
heap at its mouth. 

At Rico many of the characteristics of alluvial fans are beautifully 
illustrated. An inspection of the map will show the extent of the 
principal ones and the different relative positions of the stream chan- 
nels upon the cones, and in several cases the contouring indicates the 
lines of former channels. The typical appearance of the alluvial fans 
is shown in PI. XXI, from a photograph of the Aztec fan taken at a 
point upon the east side of the river near the wagon road. In this 
case the present channel is central. Other abandoned courses maybe 
made out in the aspens on the north side, and another exists along the 
southern edge but can not be seen in the illustration. An interesting 
feature also shown in this photograph is the smaller fan which has 
been formed in front of the larger one. From the relations exhibited 
it appears that the great fan originally extended farther to the east 
than at present, but that the river in shifting its course was thrown 
Bgainst its base and cut away its lower portion, producing the steep 
bank now exhibited. During this period of cutting the channel on 
the fan probably had a location different from the present. Since the 
channel was located at the position which it now has a secondary fan 
has been formed by material, a portion of which seems, from the 
depth of the channel, to have been derived from the upper part of 
the main fan. 

Other fans than those represented occur in Silver Creek at the mouth 
of Allyn Gulch and of the nexl gulch above upon the south side. Also 
a portion of the surface mate rials upon the hillside west of Rico may 
have been formed in the same manner as the fans of the lower valley, 
which they very closely resemble as topographic features. These have 
not been distinguished from tlie adjacent surface debris. 

Calcareous spring deposits— The Rico Mountains are well watered, 



1(34 GEOLOGY OF THE KICO MOUNTAINS, COLORADO. 

and even in the driest seasons most of the gulches contain very con- 
siderable streams which are fed by springs. The water of the springs 
is usually impregnated either with lime or with iron, probably of 
rather superficial origin, and locally these ingredients are frequently 
present in sufficient amounts to separate from solution and form depos- 
its upon the surface or in the interstices of gravel or other loose sur- 
faee materials. In some cases the waters, besides their mineral con- 
tents, are impregnated or accompanied by gases, such as sulphureted 
hydrogen and carbonic acid gas. 

The generally calcareous nature of the spring water at Rico is a 
direct result of the richness of the prevailing sedimentary formations 
of the central region in carbonate of lime, hut in most cases the amount 
of the mineral held in solution is not sufficient to give rise to important 
deposits of tufa. There are. however, several such deposits which are 
situated upon the lower slopes in localities where loose materials cover 
the solid rock for some distance above the springs. From this relation 
it seems likely that the waters travel underneath the surface of the 
ground from the higher elevations and. percolating through the loose 
surface materials, dissolve en route carbonate of lime, which they rede- 
posit upon emerging at the surface, partly by evaporation and loss 
of carbonic acid and partly through the agency of the animals and 
plants which inhabit the boggy places about the springs. The lime is 
frequently deposited in such a way that ponds are formed, and in these 
small snails find a congenial habitat, the shells of successive genera- 
tions gradually adding to the growth of the lime deposit. Moss grow- 
ing in the bogs is continually saturated in the calcareous water, and 
becomes at first coated but finally entirely impregnated with the lime, 
giving rise to a spongy mass which is often found near the lime springs. 
Grasses, leaves, and twigs falling where the water can trickle over 
them are quickly entombed, and upon decaying leave their character- 
istic forms impressed upon the resulting rock. Leaf impressions may 
be found at almost any of the springs; they are especially well shown 
in the deposits above the wagon road south of Horse Gulch. 

The principal deposit- of calcareous tufa have been outlined on the 
map, by reference to which their extent and distribution may be seen. 

At one locality the tufa has been quarried for a kiln and has found 
a considerable use. since it is conveniently located and produces lime 
of good quality. 

Ferruginous deposits. — Iron-bearing springs occur at several places 
in the Rico Mountains, and have left local deposits of iron oxide, 
cementing surface debris and forming what is commonly known as 
"iron cap." Though occurringat otherplaces, these ferruginous con- 
glomerates are especially in evidence in Silver Creek above the Fort 
Wayne tunnel, in the upper part of the northern and western branches 
of Horse Gulch, and in the lower part of Horse Gulch at the base of 



-' RECENT GEOLOGIC HISTORY. 165 

the northern landslide area. Their origin is probably connected with 
the oxidation of iron pyrites, but their occurrence can never be safely 
taken as a clue to the proximity of large bodies of that mineral. 

Gas springs. — Emanations of carbonic acid gas and of sulphureted 
hydrogen accompany many springs of water in the Rico region. The 
former is continually escaping in large quantities in the central part 
of the dome, while the latter is noted in many places on the west side 
of the mountain group in the drainage of Stoner and Bull creeks. 
Both gases doubtless have their origin in chemical changes which are 
going on at a greater or lesser depth beneath the surface, and the 
waters with which they are associated may or may not be of deep- 
seated origin. In some places they certainly are not, for in the case 
of the sulphur springs the water increases and diminishes with the 
humidity or dryness of the season, and at certain times the flow of 
water ceases entirely, but the gas continues to escape. It appears that 
in such instances the gases have found the same channels along- which 
the waters are circulating and that the two mix and escape together. 
In like manner it is notable that the carbonic acid gas, which is escap- 
ing in large quantities in various places, is far in excess of the amount 
which can be absorbed by the water with which it issues, and in mine 
workings the gas is frequently encountered where it flows up from 
crevices without any water at all. In one of the borings of the Atlantic 
(able Company, made several years ago, a flow of gas was tapped 
which, being confined, is said to have had a pi-essure of more than 50 
pounds and to have maintained it, with slight decrease, to the present 
time. A similar pressure is reported to have been shown by gas 
encountered in a borehole in the Rico- Aspen workings. 

Several tunnels in the west bank of the Dolores at Rico have struck 
carbonic acid gas escaping from many fissures in the highly shattered 
rocks in the vicinity, and a spring of water strongly charged with this 
gas bubbles up through the gravels of the river bed not far from the 
Shamrock tunnel. 

Several of the carbonic springs at Rico are locally known as "soda 
springs," and, while no analyses have been made of their waters, there 
is no reason for doubting the correctness of this designation. Their 
waters are highly charged with gas, an excess of which escapes in the 
form of bubbles, and are cool and of a delicious flavor, resembling, in 
this respect, the waters of known soda springs at other localities in 
Colorado. 



GLACIAL SCULPTURE OF THE BIGHORN MOUNTAINS 
WYOMING 



FRANCOIS F. MATTIIFS 



CONTENTS 



Page. 

Introduction 173 

Topographic conditions 174 

Climatic conditions 174 

Geologic conditions 175 

Postglacial conditions 175 

J >escription of the glaciated area of the Bighorn Mountains 175 

Recession of cirque walls 178 

Nivation 17(» 

Cause . »f glacial motion 185 

169 



I L L U S T R A T IONS 



Page. 

Plate XXIII. Map of glaciated region near Cloud Peak 176 

Fig. 1 . Preglacial topography 1 74 

2. Postglacial topography 1 74 

3. Cross section of snowdrift site - - L81 

4. Cr< iss section of a flat valley 1 S3 

171 



GLACIAL SCULPTURE OF THE BIGHORN MOUN 
TAINS, WYOMING. 



Bv Fran</ois E. Matthes. 



INTRODUCTION. 

Owing to an unusual concurrence of conditions, topographic and 
climatic, which governed the distribution and growth of the former 
glaciers of the Bighorn Mountains, this range now abounds in features 
of glacial sculpture showing great regularity and beauty of form. 
Besides being an exceptionally fruitful field for the study of cirques 
and their development, it offers a class of data which in many other 
glaciated regions are either vague or altogether absent. Tt is the 
purpose of this paper first to describe these data, and then to discuss 
their bearing on the cause of glacial motion. 

All mountain systems which are or have been centers of local gla- 
ciation exhibit numerous examples of that type of alpine valleys 
which terminate at their heads in rocky amphitheaters known as "'gla- 
cial cirques." These have been justly recognized as the main sources 
of glaciers, for the enormous quantities of snow which collect in them 
every winter, whether wind-blown or brought down by avalanches 
from I lie surrounding cliffs, constitute practically the only accretions 
to the body of the ice streams. Until lately there has been a tendency 
to regard a cirque basin as one which by its very form is eminently 
adapted to the accumulation of snow, and which from the beginning 
has had much the same shape. That glaciers may be aide to scoop 
out a cirque has been suggested by Gastaldi ' and Hellandr yet not 
until Mr. Willard D. Johnson propounded his views concerning the 
recession of amphitheatral walls by a sapping process occurring at 
the bottom <>f "bergschrunds" have we come to look definitely upon 
the cirque as the peculiar and characteristic product of the action of 
the ice mass contained within it. Accepting Mr. Johnson's explana- 
tion of this process, as seems warrantable to me in the light of inde- 
pendent investigations, we must consider a cirque as a modified, 
preglacial, stream-worn \ alley, whose V-shaped cross section lias been 



174 GLACIAL SCULPTURE OF THE BIGHORN MOUNTAINS. 



converted into a wider U-shaped one, and whose grade has been flat- 
tened rather than lowered. When, therefore, we study the present 
shape of any individual cirque the influence of the preglacial topogra- 
phy must be taken into account, In most glaciated regions, unfortu- 
nately, it is difficult to trace out the features of the preglacial 
topography. In the Swiss Alps, in Norway, and in part of the Sierra 
Nevada, as well as in Colorado, the cirques as a rule are only partly 
developed, the antecedent topography can not be restored, and no 
estimate can be made of the total change wrought by the ice in any 
particular case. In these regions it is next to impossible to find a 
cirque which may be set down as a complete specimen of the type. 
The conditions necessary for the production and preservation of such 
a cirque rarely occur in combination, as may he gathered from the 
following review. They are, first, topographic; second, climatic; 
third, geologic; and fourth, postglacial. 




Fig. 1.— Preglacial topography. 



Fig. 2.— Postglacial topography. 



Topographic conditions. — For typical cirque development the 

preglacial valleys must he situated far enough apart to admit of the 
necessary broadening in adjacent pairs without coalescence across 
interspaces. 

In most high mountain ranges the preglacial valleys were close 
together, and as a result the spurs between the present cirques have 
dwindled to mere arretes. or have altogether vanished, while the sum- 
mits and crests separating the heads of the cirques have been reduced 
to Matterhorn-like "•aiguilles ** or needles, and the lower divides to cols 
(see figs. 1 and 2). Since many alpine valleys fork near their upper 
ends, twin cirques and more complex forms often arise. 

Climatic conditions. — The summits, crests, and spurs between the 
cirques, wherever they are wide, must remain unglaciated, otherwise 
the limits of the sculpturing in each cirque will be effaced. 

In the majority of the mountain systems which at one time were 
centers of local glaciation, the precipitation was sufficient to produce 
continuous ice caps extending over a large part of the crests and spurs. 



katthes.] GLACIATED AREA. ITT) 

The line of demarcation between the work of such an ice cap and that 
of the cirque glaciers can not, as a rule, be definitely established. 
Moreover, in sueh regions as Switzerland and the Scandinavian penin- 
sula the effect of an ice sheet of continental proportions adds to the 
confusion and renders the study of cirque sculpturing still more unsat- 
isfactory. In general, whenever in any region glaciation has ceased 
to be local the pristine outlines of the cirques, as well as those of lesser 
features illustrative of the incipient stages of glacial sculpturing, will 
be lost to the student. 

Geologic conditions. — In order that regular, simple forms may lie 
produced, the rock in which the cirques are sculptured must be both 
fairly homogeneous in texture and uniform in hardness. 

The obscuring effects of concentric shelling and of pronounced cleav- 
age and jointing planes, as well as the alternation of hard and soft 
sedimentary strata, are well illustrated in the Sierra Nevada and the 
Alps. 

Postglacial conditions. — It is necessary that the characteristic forms 
left by the ice shall not he marred by postglacial remodeling. 

On account of the rapid weathering of the exposed rock of the 
amphitheatral walls and the consequent accumulation of talus at their 
bases, many of the finest cirques in the Alps and in Colorado are being 
rapidly converted into vast semicircular hoppers, while the glaciated 
Surfaces lower down in the canyons are becoming effectually concealed 
by encroaching vegetation. Postglacial stream erosion is equally det- 
rimental, and it has done much in regions like the Alps to destroy 
evidences of great value. 

When we remember that most of our knowledge of glacial cirques 
has been gathered in the Swiss Alps, in Norway, and in the Sierra 
Nevada, regions where the above-stated conditions have seldom oper- 
ated in unison, we shall better appreciate the difficulties under which 
glacialists have labored, and shall realize what an unsatisfactory Held 
for the study of cirques has so far been available. To all these 
regions the Bighorn Mountains stand in favorable contrast; indeed, 
the\ scarcely have a rival. 



DESCRIPTION OF THE GLACIATED AREA OF THE BIG- 
HORN MOUNTAINS. 

The Bighorn Mountain- form a single, broad range extending in a 
northwesterly direction from the center of Wyoming into the south- 
ern part of Montana. They consist essentially of one large anticline, 
the granitic core of which has been exposed by denudation for a dis- 
tance of about 7<» mile- along the highest part of the crest line. The 
eastern Hank rises abruptly from the plains of Wyoming, which extend 
eastward for hundreds of miles, whilethe western flank decline- much 



17() GLACIAL SCULPTURE OF THE BIGHORN MOUNTAINS. 

more gently to the broad basin of tin- Bighorn River. These plains, 
neither of which has ever been covered by the continental ice sheet, 
have a mean altitude of about 1,000 feet. The crest of the range varies 
between 8,000 and L3,000 feet in elevation. Its highest point, known 
as Cloud Peak, L3,165 feet high, is the remnant of a massive dome. 
The width of the range in this neighborhood is close to to mile-.. 

The area in which glaciation has taken place extends for over 30 
miles alone the crest. The accompanying map (PI. XXIII). prepared 
during the summers of L897, 1898, and L899,shows the greater part of it. 

None of the trunk glaciers which flowed from this region ever 
reached the plains; the longest one. that in the valley of West Ten- 
sleep Creek, had a length of Is miles, its farthest terminal moraines 
being at an altitude of 6,900 feet, or nearly 5,000 feet below the floors 
of the highest cirques at its head (see L3 and is. PI. XXIII).' 

By far the most conspicuous features of the area mapped are the 
dee)) glacial canyons, with their precipitous amphitheaters, contrast- 
ing strongly with the smooth outlines of the summits between them. 
Those which appeal to the tourist most and offer the finest scenic 
effect are situated north of peak- A. B, and C. The magnificent can- 
non 7, cutting through no less than three peaks; the almost isolated 
table a: the fantastic comb ridges or arre'tes, and the pinnacle- of the 
main range form a group of topographic feature- worthy of a pil- 
grimage. The most fruitful field for study, however, lies among the 
rounded summits, crests, and -pur- of that part of the range between 
the headwaters of Tensleep and ( Hear creeks. For, \\ bile the cirques 
north of B and C have developed in parallel valleys situated side by 
side, and have consequently interfered with one another in their 
broadening, those numbered 23, 24, •_'■">. '■'<■'<. '■'<*. '■>■>. '■'<■'. etc.. remain 
separated by broad, massive -pin-, and have developed unhindered to 
their full extent. Some, it is true, such a- 22, 23, :'•■"•. are complex 
forms, owing to the forking of the preglacial valleys, hut the others 
are of simple, often straight form: thej may lie termed orthotypical 
(see 25, 39). Besides, a close inspection has shown thai the summits^ 
cre-ts. and spurs between them have never suffered glacial erosion; 
that is to say, there has never been a continuous ice cap on this range. 
Consequently the outlines of these cirques and canyons arc strictly 
the products of the sculpturing done by the ice in each of them, and 
the intermediate surfaces are virtually representative of the pre- 
glacial topography. Here. then, the topographic and climatic condi- 
tions have combined in a manner most favorable for study. 

While humps and irregularities of minor impo 1 mce abound in 
the larger canyons, those numbered 22, 23, 25, •">'.». are singularly free 
from them. The granite in which 25 and :'.'.» were hewn out is fairly 
homogeneous; its joint- run in various directions and do not affect the 



1 The ]>caks and spurs referred to are 1' em p in alphabetical on er from north 

while the cirques and other valh Imilar manner. 



matthes] FEATURES OF THE GLACIAL CIRQUES. 177 

shapes of the cirques. In 17, 19, 41, the inclination of the joint planes 
has resulted in the production of a steeper grade than usual, while in 
the case of the cirques on the east and west faces of Cloud Peak the 
-lecj) dip of the joint planes has caused the cliffs to he more nearly 
vertical than elsewhere. Yet in general form and outline none of the 
eiii I ues can be said to greatly differ. On the whole, then, the geologic 
conditions also are favorable. 

Nearly all of the cirques shown on the map are in a good state of 
preservation. The crumbling of the walls by postglacial weathering 
has not been extensive enough to materially change their aspect, and 
the accumulation of talus is correspondingly moderate. The canyon 
33 has. perhaps, suffered most in this respect; its upper end is now 
once more V-shaped on account of the talus slopes. In 20 these have 
just begun to meet. Not ten years ago a well-worn pack trail extended 
up this valley and passed over the divide into the Tensleep Creek drain- 
age. This trail has now been abandoned as impracticable. On the 
other hand there are many localities where the talus is insignificant, 
as, for instance, at f, and in canyons 10, 12, 21, 22, 23, 25, 39, and 
others. 

Postglacial stream erosion has been very slight. It has effected no 
appreciable changes in the granite floors of the cirques and canyons, and 
its most important results are found in the silting up of small morainal 
ponds. While the valleys formerly occupied by the trunk glaciers, since 
they are floored with morainal material, are now covered by dense pine 
forests, the cirques and canyons, us well as the spurs between them, are 
all situated well above the timber line, which closely follows the 10,000- 
foot contour. For reasons which will appear later, occasional patches 
of alpine scrub fir and dwarf willows, as well as grass, flowering plants, 
and moss, rind nourishment on the high, unglaciated surfaces; but the 
floors of the glaciated cirques and canyons are virtually devoid of all 
vegetation or humus. Their features are, therefore, left wholly 
unmasked by the products of organic agencies. 

From the, foregoing brief description it is apparent that the four 
conditions essential to the production and preservation of complete 
cirques— that is, of features of glacial sculpture generally, did in a large 
measure obtain in the Bighorn Mountains. The original valleys were, 
in places, far apart, and the cirques which have since formed in them 
have developed undisturbed; the structure of the rock has been favor- 
able to the evolution of simple forms, and, on account of the absence of 
an ice cap, the present extent of each cirque is truly indicative of the 
sculpturing done within it. 

The changes wrought by the postglacial agencies — weathering, 
erosion, and vegetation, which have been so active in obliterating the 
glacial features of the Alps- are here as a rule too insignificant to 
complicate the investigation, 
21 GEOL. pt 2 12 



178 GLACIAL SCULPTURE OF THE BIGHORN MOUNTAINS. 

RECESSION OF CIRQUE WALLS. 

At the annual meeting of the Geological Society of America, held 
December 28, 1898, 1 Mr. Willard D. Johnson presented a theory in 
explanation of the recession of the amphitheatral walls of cirques, 
ascribing it to "sharply localized and abnormally vigorous weathering," 
by rapid alternation of freezing and thawing at the exposed bottoms 
of "bergschrunds." According to him, the effect is essentially that 
of sapping the walls at their base, thus causing them to recede. 
Similar action at the bottoms of those transverse crevasses which 
occur where the glacier loses its continuity over the edges of cross 
benches produces the recession and accentuation of these benches. 
Since the effect of a continuous ice mass of great thickness is to 
protect its bed against oscillations of temperature, maintaining it at 
32° F.. this explanation seems a rational one; for, while on the one 
hand the recession of the cirque walls can not be due to scour, and 
is essentially the result of a quarrying process, on the other hand the 
"bergschrunds" proper as well as the lower transverse crevasses are 
the only channels through which the air, with its fluctuating tempera- 
ture, is admitted to the bed of the glacier. While we have no experi- 
mental data upon this point, yet it is reasonable to assume that, on 
account of the water running in subglacial channels, a downward 
draft is produced in the "bergschrunds" and the other crevasses in 
much the same manner as in the manholes of a sewer. 

Close investigation of the floors and terminating walls of the glacial 
cirques in the Bighorn Mountains fully bears out Mr. Johnson's views. 
Step-like transverse benches occur in many of the canyons shown on 
the map, notably in those marked 8, 9, 10, 12, 17, 18, 19, and 31. The 
cirque walls appear plainly to have receded on account of a quarrying 
process, while on the other hand the lower parts of the canyons appear 
merely to have been scoured out by the passing ice. In some cases the 
recession of opposing cirque walls has reduced the divide between 
them to a thin arrete (see 7 and 8 and 7 and 10); in other cases these 
arrctes have been leveled down to cols, as between 8 and 9, 12 and 13, 
and 20 and 21. In the latter instance this has resulted in the capture 
of the drainage of 18 by 20. 

Recession there has been, bevond a doubt. The question is, how 
great a distance has been covered by cliff recession in any particular 
case; in other words, what was the original point in any valley at which 
a cirque first began to develop;! Must we suppose, in the case of can- 
yon 7, for example, that the cirque wall has receded from the canyon 
mouth clear back to its present site, a distance of over 2 miles % Or must 
we assume that the cirque formed at the head of the preglacial valley, 

i For abstract see Science, new series, Vol. IX, 1899, pp. 106 and 112-113. 



MATTHES.] NIVATION. 179 

carrying it back toward the divide, and that the greater part of the 
canyon is the product of glacial scouring ? A comparison of the cirques 
on the map reveals that, while the cirque walls of 7, 8, 9, 10, 11, 12, 
13, 15, etc., have receded beyond the heads of their respective valleys, 
those of 14, 18, 28, 29, and 31 have not done so, for the upper ends of 
the preglacial valleys still remain unglaciated above the present sites 
of the amphitheaters. (The cirque walls in 28 and 29 are not hign 
enough to appear distinctly on the map, owing to the large contour 
interval.) It is evident, then, that a cirque does not necessarily form 
at the head of a preglacial valley, but originates at the highest point 
in it which satisfies the conditions indispensable to its development. 
These conditions, whatever the} r be, did not obtain in the upper parts 
of 14. 18, 28, and 29, otherwise thej r also would have been glaciated. 
If parts of valle} r s can remain unglaciated, should we not expect to find 
entire valleys similarly exempt? Such unglaciated valleys do indeed 
occur in these mountains, and they are the more striking where they 
are situated amidst the deepest and most heavily glaciated canyons 
(see 3, 4, 26, and 27). They were undoubtedly subject to the same 
climatic conditions as the neighboring canyons; 26 and 27 must have 
shared the same mean annual temperature and the same snowfall with 
the preglacial valley 25. There must then have been other circum- 
stances which determined what valleys should become glaciated; that 
is to say, whether cirques should develop in them; and if so, at what 
particular places. 

Before pursuing this inquiry further, it will be helpful to first study 
in detail the character of these unglaciated surfaces. 

NIVATION. 

We have thus far described the rounded summits, crests, and spurs, 
also the valleys just mentioned, as "unglaciated." They do not, in 
fact, offer the slightest evidence of glacial scour, and are, as a rule, 
densely littered with rock disintegrating in situ. 

It would nevertheless be absurd to suppose that these large areas 
remained bare throughout the period of glaciation. Even now, when 
the large glaciers which once tilled the canyons have almost vanished, 
large snowdrifts accumulate every winter on the unglaciated slopes. 
A single severe winter is capable of producing snow banks which all 
the heat of the ensuing summer can not remove. According to my 
own observations the snowdrifts of the exceptionally severe winter 
of 1898-99 were still from 25 to 50 feet deep and often 1,000 feet long 
at the close of the following summer in places where I had found no 
trace of snow the preceding year. A number of these drifts were on 
slopes having a southern exposure. Most probably, therefore, in 
glacial times a layer of neve covered the greater part of this ungla- 



180 GLACIAL SCULPTUKE OF THE BIGHORN MOUNTAINS. 

dated area, more especially its depressions, and since there is no evi- 
dence of scour or of transportation of loose-rock debris it is to be 
inferred that this neve mass remained quiescent. That this inference 
is borne out by another class of evidence I shall now endeavor to 
show. 

While 1 was traveling over the smooth, grassy slopes of that part of 
the Bighorn Range locally known as the Bald Mountain district, which 
lies outside of the glaciated area and is peculiar on account of its 
large and smoothly rounded features, my attention was repeatedly 
attracted by certain bare and desolate-looking areas, the exposed soil 
of which contrasted strikingly with the green of the surrounding sod. 
They were each invariably associated with some more or less marked 
accident in the slope of the mountain side, and they were generally 
situated on slope- having a northeasterly exposure. A clew as to the 
reason of their occurrence soon presented itself. A Dumber were 
found partly covered with the remnants of snowdrifts, fast disappear- 
ing under the July sun. These drifts had no doubt accumulated in 
the lee of the escarpments and swells againsl which they were invari- 
ably situated. The prevailing winds being southwesterly in this region 
the northeasterly slopes naturally offer the most favorable conditions 
for the formation of such drifts. These, therefore, recur upon the 
same sites periodically and modify the surface configuration suffi- 
ciently to render them conspicuous. 

Observations on a number of drift Bites, as well as on drifts of all 
sizes and in all stages of ablation, disclose the following facts: 

1. The soil exposed by the retreating edges of the drift appears 
loosened up. porous, and crumbling. 

2. A layer of exceedingly tine mud is deposited on the lower portion 

of the site, especially at the toe of the drift. 

3. The site is devoid of drainage lines; that is, it shows no effects 
of concentrated erosion in well-defined channels. 

4. The site is more or less sunk into the face of the slope the steeper 
the slope the more pronounced the depression. 

5. The slope of the site tends to become concave in profile as well as 
in horizontal contour. 

6. There is no indication of scour or of transportation of material as 
if by movement of the snow mass. 

The looseness of the soil around the drift must be attributed to 
frequently recurrent frost action. The drift acts as a blanket in pro- 
tecting its bed from oscillations of temperature, but the water derived 
from melting at its edges on summer days naturally permeates the soil 
in the immediate vicinity. This zone of water-soaked soil is exposed 
to those sharp frosts which at such altitudes occur regularly each 
night, except during a few week- i,, August; and as the edges of the 
shrinking snow mass retreat new portions of its site are thereby 



MAn„,,>.| NIVATTON. 18] 

exposed. Owing to the oft-repeated distending action of freezing 
water in the capillaries of the soil, the latter loses its cohesion and 
becomes finely divided. Upon thawing, the soil water carries with it 
a portion of the tine material thus loosened for such distance as it may 
have transporting power. Since their are no well-worn channels on 
any of the sites inspected, it may be inferred that the water from the 
upper edges of the drift percolates slowly under the mass in sheets 
without exerting appreciable erosive power. This fact was particu- 
larly well demonstrated on some sites visited by me, from which the 
snow had almost disappeared, and on which the water-soaked and 
porous soil could still be seen undisturbed, presenting a somewhat 
honeycombed appearance, devoid of eroded channels. It was barely 
passable on foot. 

The steeper portions of a snowdrift site, whenever exposed to frost 
action as described, have a tendency to become accentuated as the loose 
material is carried down by water, or to crumble. A drift lying against 




sitiini hi escarpment <l i 



a deep escarpment will, therefore, in time accentuate the slope thereof, 
and if the drift occupies but a small portion of a slope its site will 
tend to become depressed (see tig. 3). This would naturally he less 
pronounced in the case of flat or gently sloping sites. Owing to the 
frequent oscillations of the edge and the successive exposure of dif- 
ferent parts of the site to frost action, the area thus affected will have 
no well-defined boundaries. The more accentuated slopes will pass 
insensibly into the flatter ones, and the general tendency will be to 
give the drift site a cross section of smoothly curved outline, and 
ordinarily concave. Furthermore, the retreating edge of a snowdrift 
of any thickness tends to assume a rounded outline, ablation being 
unfavorable to the production of sharp corners or of angularity of any 
kind. The outlines of drift sites will therefore tend to have a similar 
form, and, since an ordinary drift site is hollow to begin with, the 
result is in general that its slopes are concave in profile as well as in 
horizontal contour. 



182 GLACIAL SCULPTURE OF THE BIGHORN MOUNTAINS. 

That snowdrifts have no sliding- motion appears certain in view of 
the fact that no signs characteristic of such motion are to be found on 
any site, and that even the finest soil under them remains in place. 

From this rather brief study of snowdrifts and their sites we infer: 

1. That snowdrifts do not form except in the presence of favorable 
topographic features. 

2. That the effect of their presence is to accentuate these features by 
frost action at their peripheries. 

3. That they tend to protect their sites against aqueous erosion. 

4. That they favor the formation of deposits of line mud. 

5. That they have no sliding motion. 

To return to the unglaciated slopes and valleys, which, as we have 
reasons to believe, were largely covered with quiescent snow or neve, 
let us now see whether they show any effects similar to those produced 
by snowdrifts. 

All the high peaks and slopes, which on the map appear so strangely 
.smooth of outline, possess an extremely rough surface in detail, toil- 
some to climb. Rapid weathering at the joint cracks has loosened 
vast numbers of angular blocks oi granite of all sizes. Whereverthe 
slope is at all steep line material is not retained, and as the climber 
lift- himself from one block t<> another the sound of trickling water 
reaches him from the depth of the gaping holes under his feet. 
Wherever the slope is comparatively flat, the blocks are embedded in 
a thick layer of soil and small angular fragments, covered with moss, 
or. on the lower reaches, with grass and patches of alpine scrub fir. 
The flanks of peak-, such a- A. I). E, I". (i. and the summits of the 
main range farther south are essentially made up of steep, rocky slopes 
and irregular benches of line material, alternating with each other, 
but of so little prominence a- not to influence the shapes of the 
masses. That these benches are favorable to the formation of snow- 
drifts is demonstrated by the fact that even now many drifts collect 
on them every winter. I had several opportunities during the falls 
of L898 and 1899 to watch I he effect of snowstorms on these peaks. 
Their appearance at the end of each -torm was a mottled one, the 
benches presenting a brilliant white, while the rocks on the steeper 
slope- between remained mostly bare. Long after the snow had dis- 
appeared from the latter the drifts on the benches were still present. 

The neve which once lay on these peaks must be considered as hav- 
ing been made up of a large number of drift-, each occupying a bench 
and producing thereon the presenl layer of line material, partly by 
preventing that already there from being carried away by water, and 
partly by arresting the mud brought from under the blocks on the 
steeper slope above it. 

Even the most casual observation suffices to impress one with the 
smoothness and the delicate green color of the surface of such valleys 



MATTHES.] NIVATION. 183 

as 3, 4, 5, 10, 26, and 27, in contrast with the rough and brown spins 
between them. They afford the best traveling to the mountaineer, 
the rocks being embedded in a compacted mass of small, angular debris 
and mud, a natural macadam, as it were, such as may be found on the 
benches on the peaks. Their cross section is generally of a shallow 
cup shape, and numerous rills take the place of a central channel, 
which begins to appear only in the lower portion. Wherever the 
debris is loose the courses of these rills are marked merely by narrow 
strips devoid of soil and vegetation, the water trickling under and 
between the fragments. In other places, where the debris is more 
compact, the water remains at the surface and its channels are choked 
with moss. T encountered many large drifts in valleys of this descrip- 
tion, and there can be no doubt that their characteristics are largely 
due to the presence of quiescent neve at the time when the neighbor- 
ing cirques were tilled with large glaciers. 

If we consider their original cross section as flat V-shaped (fig. 1), 
disintegrated rock on those parts of the two slopes, which, owing to the. 
frequent oscillations of the edges of the neve mass, were exposed to 




FIG. 1.— Cross section of a flat valley. Dotted line shows new surface produced by nivation. 

frost action, would be loosened and carried down under the drift, to 
be deposited at the bottom of the cross section. From our observa- 
tions on existing drifts we know that stream erosion is arrested under 
the neve; the central channel would therefore gradually till up with the, 
material brought down from either side and tend to become obliterated. 

The effects of the occupation by quiescent neve are thus to convert 
shallow V-shaped valleys into flat U-shaped ones and to efface their 
drainage lines without material change of grade. These neve effects, 
which are wholly different from those produced by glaciation, I shall, 
for the sake of brevity, speak of as effects of n! nation, the valleys 
exhibiting them having been nivated. 

Examples are numerous. The finest may he found on the east side 
of the peak A, on the flanks of G, and above the amphitheaters of 14, 
18, 28, 29, and 3.1. Of particular interest are the wide and smooth 
depressions northwest and southeast of E and F, in which the original 
drainage lines have completely disappeared, and have been replaced by 
shallow rills choked witli grass and alpine dwarf willows. The wide 
flat 6 is of less value in (his connection, its surface being too irregular 
and broken. Its lower portion is covered with lateral moraines sup- 
porting a dense forest, and has thereby been converted into a veritable 



184 GLACIAL SCULPTURE OF THE BIGHORN MOUNTAINS. 

wilderness. By far the most remarkable example of oivation exists 
at 2, a largo expanse of grass and willows, swampy and treacherous, 
sloping up in gentle, sweeping curves to the encircling sharp crests 
and pinnacles. The glacier which once flowed past this bench barely 
reached to its lower edge, and did not deposit any moraines upon it. 
The tops of the highest spruce trees along the timber line, which 
coincides very nearly with the lateral moraines, are just visible above 
the edge of the lint. 

A glance at the nivated areas just described impresses one strongly 
with their general smoothness and the wavy outlines of their features, 
which stand in marked contrast with the broken surface and angularity 
of the glaciated canyons and cirques. 

Intermediate between these two types of topography is a third, more 
variable perhaps, and less easily described, which, to some extent, par- 
takes df the nature of both. It i> best typified in the region near the 
headwaters of Little Goose and North Piney creeks. Along the crest 
of tin- range between t hoc two creeks are many cirque-like valleys 
separated l>\ narrow, angular spur-. They are deeper than those 
which we have jusl considered, and at the same time they can scarcely 
he classed with such pronounced canyons as 7 and 25. In them we 
find the evidences of nivation alongside of those of true glaciation, 
the latter usually on a small scale. At the very head of Little Goose 
Creek are two cirque-like valleys which maybe regarded as typical 
of this class. The amphitheater walls are nol pronounced, nor could I 
find any sign- of glacial motion, such a- si nation. There i-. howe\ er, 
a small amount of morainal material, not in distinct heaps but rather 
spread out. lower down in the valley. On the other hand the bottoms 
of the cirques are not clean swept, but are liea\ il\ cumbered \\ ith line 
material. Postglacial talus was present in such small quantities, 
especially in No. l. and looked so fresh, that it was easily distinguish- 
able. We must infer from this that true glacial motion existed only 
duringa short time in the neve occupying these valleys, and that most 
of the time it remained quiescent and acted like a large snowdrift. Il 
may be considered as a case of incipient glaciation. Similar conditions, 
though less distinct, exist in some of the smaller valleys to the north- 
east, until finally we find some in which no signs of glaciation can be 
traced at all. only •"nivation"' being in evidence. In this manner gla- 
ciated forms are seen to shade out into nivated forms; and it is possi- 
ble to establish a complete series of gradations from the deepest gla 
ciated cirque to the most featureless nivated Hat. 

However interesting these eases may he. the\ are not bo instructive 
as another category of valleys, much more numerous in these moun- 
tains than any of those yet described. Those marked 28, 2'.*. and In 
are typical examples. Their upper ends are solely nivated. while 
their lower ends are undoubted^ glaciated and well scoured out. 



matthes.] THE BERGSCHRUND. 185 

Iii some (as in 29) the line of demarkation between the two processes 
is easily found, there 1 being :i small cliff resembling more or less an 
amphitheater wall. In others, however, especially those whose increase 
in depth is very gradual, there is no sharply defined boundary to be 
found; there is apparently a short stretch over which the neve some- 
times slid and sometimes remained stationary. In general, the more 
rapid the increase of the depth of the valley, the more distinct is the 
boundary line between the nivated and the glaciated areas. 

CAUSE OF GLACIAL MOTION. 

A cirque is essentially the product of a "bergschrund." Were it 
not for the opportunity this great crevasse offers to the outside air to 
reach the foot of the cirque wall, the latter would have no tendency 
to recede; indeed, no cirque would form at all. Every amphitheater 
shown on the map must therefore be regarded as an indication of the 
former existence of a "bergschrund," paralleling the curve of its 
head wall and opening to its foot. 

The "bergschrund" itself is merely a crevasse, or a line of crevasses, 
which extends along the cirque wall and opens every spring by the 
motion of the neve on its downstream side. Sometimes, it is true, 
there are two or more parallel lines of crevasses, produced by trans- 
verse benches near the head of the cirque; but in the most nearly 
perfect cirques the " bergschrund " is one single rent. A beautiful 
example exists at the head of the small glacier on the east side of 
Cloud Peak. 

We have seen that in valleys like 1-f, 18, 28, 29, and 32 the evidences 
of glacial motion, such as scouring and polishing of the bed, extended 
as far up as the cirque wall; above it there are only signs of nivation. 
The "bergschrund" constitutes, then, the dividing line between the 
moving neve and the quiescent neve; it is the upper limit of glacial 
motion — that is, it indicates that place in any valley above which (he 
conditions essential to the production of glacial motion cease to exist. 
The law governing the location of the "bergschrund" is, therefore, 
intimately connected with the cause of glacial motion. 

It has been suggested by Rev. Coutts Trotter 1 that the lower layers 
of a neve, mass musl be raised to the melting point in order that they 
may slide over the bed. The "bergschrund" would, then, mark that 
line above which the necessary temperature conditions do not exist, 
the neve remaining stationary and perpetually frozen to the ground. 
According to Mi - . Trotter, the " bergschrund" would coincide with an 
isothermal surface, that of the mean annual temperature of 32° F., 
and one might be led to conclude that the upper limit of glacial motion 
is, at any point, determined by the elevation of the spheroid of 32° F. 



!!..> . s. ..-.. lssr,. Vol. XXXV 



186 GLACIAL SCULPTURE OF THE BIGHORN MOUNTAINS. 

This, however, seems wholly unwarranted. The fact that the mean 
annual temperature at any place is 32° F. does not preclude the occur- 
rence of periodical thaw; indeed, it rather implies it. The stationary 
neve described by Mr. Trotter as having little depth does not neces- 
sarily i-emain below the freezing point throughout its mass summer 
and winter; it does melt away on the lower peaks and arretes. as may 
be seen on the Swiss Alps. Vet it does not slide, glacier fashion. 
even then: it remains quiescent, frozen or not frozen. Whether the 
quiescent neve in the Bighorn Mountains was at one time permanently 
frozen to the ground it is difficult to determine. The effects of luxa- 
tion, which imply recurrent thaw, may have been produced only at 
the beginning of the period of glaciation. and again toward lis end. 
Certain it is, however, that no motion occurred in these neve masses 
at any time, even when considerable melting took place and nivation 
was proceeding most actively. The map shows us that quiescent neve 
did not occur above the "bergschrund" alone. The effects of glacia- 
tion and nivation are found side by side at all elevations from L0,000 
feet up, with both northerly and southerly exposures. There is even 
a case where quiescenl neve occurred lielow the terminus of a short 
glacier, namely, at 31, where the lowest terminal moraines are situated 
near the 10,400-fool contour, while the effects of nivation continue for 
more than half a mile farther down the valley. If the temperature 
conditions at this altitude were sufficient to check the advance of the 
glacier by ablation, the quiescent neve in that neighborhood certainly 
can not have been frozen to the ground, but most likely disappeared 
entirely every summer. 

If the "bergschrund" coincides with some tixed isothermal surface, 
such as the spheroid of :;•_' F. or that of perpetual frost, how are we. 
for example, to account for the occurrence of two " bergschrunds," 

one some 80" feet above the other (see 12a and L2b), or for the fact 

that the upper cirque still contains an ice mass possessing all the prop- 
erties of a glacier, while the neve in the lower ony has entirely disap- 
peared? And why has there never been any "bergschrund" at all in 
valleys like 26 and L'T. alongside of such a prominent instance of gla- 
cial sculpture as 25? If the quiescent neve* was ever permanently 
frozen in the nivated areas, many of the " bergschrunds" must have 
been situated well above the spheroid of perpetual frost. Vet there 
is no difference between cirques formed at an elevation of L2-,000 and 
those at 10,000 feet; there is no evidence that the quarrying process 
in the highest cirques has been less vigorous than in the lowest ones. 
They may all have been situated in the region of perpetual frost. 
like those of the Mount St. Elias region, which occur at elevations 
of 13,000 feet and over. The sculpturing effect is not different from 
that which can be observed in the lowest cirques of the Alps, from 
which glaciers still emanate. In short, it matters not what the mean 



matthes] CAUSE OF GLACIAL MOTION. 187 

annual temperature of the air is at the " bergschrund," the tempera- 
ture at the bottom of the glacier is constant, and whatever frost 
action takes place at the foot of the "bergschrund" is due to the 
periodical fluctuations of temperature of the outside air. 

We may conclude, then, that the location of the "bergschrund" is 
determined irrespective of any isothermal surface and that atmospheric 
temperature docs not operate as a factor in the production of glacial 
motion. 

The snow line on any mountain range is that line at which ablation 
equals precipitation. The influence of terrestrial heat, of warm air 
currents, and evaporation at great altitudes being so slight as to be 
negligible, the sun is there virtually the only source of heat operative 
in the removal of snow. At the elevation of the snow line, then, the 
total amount of solar heat received during the year is just sufficient to 
melt the entire annual snowfall; and since the latter varies with the 
humidity of the climate, the snow line will, other things being equal, 
be higher in a dry region than in a moist one. For regions having 
the same annual snowfall it is a line of equal caloric conditions; but 
it is not necessarily coincident with any particular isotherm, for the 
mean annual temperature at any place is no function of the amount 
of solar heat received by it during the year. It follows, then, that 
there is no fixed relation between the lower limit of perennial snow 
and any isothermal spheroid, and the conditions obtaining at the snow 
line on any mountain range must be considered as peculiar to the 
locality. 

In the region of perpetual snow, part of the snowfall of one winter 
is still on the ground at the beginning of the next one. As the accu- 
mulation of snow proceeds, the entire area above the snow line must 
in the course of time be converted into a vast neve field, and more or 
less extensive glaciation takes place. Complete glaciation — that is, 
occupation by a continuous ice sheet produced by the confluence of 
many minor glacial streams— is not, however, the invariable result. 
While examples of it maybe seen in Greenland and the arctic lands 
to the west of it, and others are known to have existed both in Europe 
and on this continent, it is manifestly not a universal occurrence. In 
many mountain regions a local ice cap of small extent has existed 
within the limits of the area of perennial snow; in some cases such an 
ice cap has been totally absent. The actually glaciated part of such 
a region is but a very small fraction of the entire area situated above 
the snow line. In the Bighorn Mountains glaciation has remained 
confined to certain valleys only; and, as we have seen, such a thing as 
a continuous ice cap has never covered their crest. Undoubtedly all 
the nivated areas were situated above the snow line; they were once 
buried under a thick layer of neve; yet no glaciers ever flowed from 
them, and no cirques were ever sculptured there. What, then, caused 



188 GLACIAL SCULPTUKE OF THE B1GHOKN MOUNTAINS. 

the neve in these areas to remain quiescent while glaciers from LO to 
18 miles in length flowed in the neighboring canyons ? The nivated 
and glaciated areas shared the same snowfall and the same climatic 
conditions, and if these were favorable to the production of glaciers 
in the one case, they must have been equally favorable in the other. 
Moreover, we have satisfied ourselves that the location of the amphi- 
theaters — that is, of the " bergschrunds " — is not dependent upon 
or in any way connected with temperature conditions. That being 
the case, the only other explanation that suggests itself is that the 
distribution of the glaciers was wholly governed by conditions of a 
topographic nature. 

Drifting snow collects wherever a topographic feature produces 
eddying of the wind; and the tendency of a drift is, in general, to 
Completely fill the space in which eddies occur (for winds of one direc- 
tion) until its surface is such as to be continuously wind swept 
throughout. This surface may subsequently be changed by winds 
from other directions, especially if the snow remains dry and light; 
and readjustments will continually occur as long as it remains in that 
condition and whenever it receives additions to its mass. If deposition 
continues in excess of ablation there must come a time when the snow 
completely buries the features of the topography, and their influence 
upon the distribution of the snow will no longer be fell. There is then 
for any type of country a minimum snow tall necessary to neutralize the 
distributing power of it- topographic features. Whenever the annual 
snowfall is greater than this minimum, it will produce in the course 
of time a continuous neve or ice cap. which may have glacial motion 
in any or all of its parts. A.S long as the annual precipitation falls 
short of this amount, drifts of limited extent and depth will result — 
that is to say. their location and horizontal dimensions will be con- 
formable to the contours of the ground and their vertical dimensions 
to its profile. Especially will this be the case on the elevated slopes 
of a high mountain range, where the snow remains dry and powdery 
for some time and where high winds are prevalent from one direction. 

From our studies of theeffectsof nivation we know that the nivated 
valleys have undergone but little change. We may safely consider 
them in this discussion as identical with the preglacial forms. As the 
contour map shows, they are without exception shallow. Their cross 
sections are usually less than loo feet in depth; and whenever they 
exceed that amount their width is so great in comparison that they 
can scarcely be termed deep. 'Hie nivated areas in general present 
fairly smooth, rounded features, devoid of any abrupt accident: their 
configuration throughout is such as to offer no opportunity for the 
accumulation of snowdrifts of great thickness. In areas of this type 
it seems to me beyond doubt that the depth of the neve nowhere 
exceded that of the valleys. The climate of central Wyoming is a 



ERRATUM. 

[Twenty-first Annual Report United 8tate.s Geological Survey, Part II.] 
On page 189, second paragraph, eleventh line, for "east spur of h" 
read: east spur of H. 



matthks.] CAUSE OF GLACIAL MOTION. 189 

semiarid one, and while the .snowfall in the Bighorn Mountains is 
much greater than on the adjacent plains, yet it is .small in comparison 
with that occurring in the mountains of Washington, Oregon, and 
California. Even at the time of maximum glaciation it must have 
been rather limited. At all events it was not sufficient to counter- 
balance the distributing power of the topographic features; and, 
that being the ease, the depth of the neve must have been limited by 
the depth of the valleys. Besides, it is quite probable that vigor- 
ous ablation took place in summer during the greater part of the 
period of glaciation, if not at all times. The nivated benches on the 
flanks of the peaks indicate frequently recurrent frost action due to 
oscillations of the neve edge; they must have been periodically bared 
by ablation. It seems likely, then, that ablation was a powerful agent 
in reducing the neve masses, and that it combined with the peculiar 
topography, the prevailing winds, and the moderate snowfall in pre- 
venting the neve from acquiring any considerable depth in the nivated 
areas and from forming a continuous ice cap on any part of the range. 

Turning now to the glaciated canyons, we find great depth a con- 
spicuous and ever-present feature. The majority are over 1,000 feet 
deep, and even those like 28, 29, and 40, in which the effects of gla- 
ciation are least pronounced, have cross sections several hundred feet 
in depth. The thickness of the ice masses which the} r once contained is 
easily gauged from the abrasion shown at such corners as h and i, and 
along the edges of the table a. The glaciers in the adjacent can- 
yons must have been from 1,000 to 1,500 feet thick. Those issuing 
from canyons 13 and 1-1 were high enough to overrun the spur g as 
high as e. Their combined stream must have been enormous, for on 
reaching the east spur of h it split into three bodies, one flowing 
toward Lake Solitude, abrading the north side of H as high as the 
10,800-foot contour, another overflowing into the valley of Buckskin 
Ed Creek for a distance of 4 miles, and the remainder turning south 
down the valley of West Tensleep Creek, forming, with other tribu- 
taries, a trunk glacier 18 miles long. 

The difference in depth between the glaciated canyons and the 
nivated valleys is obvious from the map alone; but while the latter are 
fairly representative of the preglacial valleys the former have been so 
extensively altered by glaciation that it is difficult in most instances to 
form a conception of their preglacial aspect. The recession of the 
cirque walls and the flattening of the grades have deepened these can- 
yons considerably, especially toward their heads, and it would there- 
fore be unwarrantable to fix the depth of the preglacial valleys by any 
measurements now obtainable. Nevertheless it seems certain that 
they were very much deeper than any of the nivated valleys and 
offered opportunity for the accumulation of great depths of neve; 
and we infer that, in general, the depth of a valley, or. more strictly, 



190 GLACIAL SCULPTURE OF THE BIGHORN MOUNTAINS. 

the depth of the ne , e in it, had much to do with its glaciation, and 
consequently with the location of the "bergschrund." In eases like 11 
and 18 there is little doubt that the upper portions remained nivated 
solely on account of their shallowness, and that the cirques began to 
form at the highest place in each valley at which the neve attained the 
minimum thickness necessary for the opening of a ••bergschrund" — 
that is to say, for the production of glacial motion. While in these par- 
ticular valleys the depth of the cirques is not representative of that 
minimum depth, on account of the recession of their walls, there are 
a few valleys, such as 2S, jj!>, 40. etc., in which a fair estimate can be 
obtained. In them thereare no marked cirque walls, and the " berg- 
schrunds" seem to have oscillated over a short stretch. As a result 
there has been little excavation and the present grade of the valley is 
nearly what it was in preglacial times. The depth of these valleys 
increases from nothing at the head downward. The thickness of the 
neve most probably increased similarly, and at the site of the "berg- 
schrund" must have occurred the greatest thickness at which neve'can 
remain quiescent that is, the minimum thickness required for the pro- 
duction of glacial motion on that grade. It will he safe to assume 
that thickness as little Less than the depth of the valley at that point. 
According to estimates made on the ground and borne out by the 
map, this thickness appeals to have been bet ween LOO and L50feet On 
a grade of about L2 per cent, therefore, neve must attain a thickness of 
at least L25 feet in order that it may have motion. While undoubt- 
edly the minimum thickness must vary inversely with the percentage 
of the grade, it is impossible to ascertain the law ,,( its variation 
without a number of additional measurements on valleys of different 
grades. For this, however, there was no opportunity in the Bighorn 
Mountains. There is good reason to believe that the influence of the 
grade is inconsiderable; the sliding of the lowesl layers of the glacier 
over its bed is really only a subordinate feature of its motion, and it 
is probably influenced more by the amount of "round moraine present 
than by the grade. 

All the evidence obtained in this region, however, leads unavoidably 
to the conclusion that the only factor which determines the location of 
the "bergschrund" in any valley is the depth of the neve. The cause 
of glacial motion, therefore, is to be sought in the weight of the ice 
mas-. That it acts independently of the temperature of the air is 
demonstrated by the fact that ''bergschrunds" open at all elevations 
and in the coldest climates. How glacial motion itself is effected, what 
processes are involved in it. and how it may be accelerated by thaw, 
are inquiries beyond the scope of this paper. 



THE ESMERALDA FORMATION, A FRESH-WATER LAKE DEPOSIT 



II. VV. TURNER 



WITH A DESCRIPTION OF THE FOSSIL PLANTS, BY F. H. KNOWLTON 
AND OF A FOSSIL FISH, BY F. A. LUCAS 



CONTENTS. 



Pago. 

< reneral description of the region 197 

( lharacter of the beds 198 

Area! distribution of the beds 198 

Thickness of the beds 199 

Details of the sections 202 

Age of the lake beds 203 

Relation of the lake beds to the lavas of the region 205 

Win deposits of the formation 206 

Economic deposits of the formation 206 

I !oal 206 

Sulphur 207 

Fossil plants of the Esmeralda formation, by F. H. Knowlton 209 

Introduction 209 

Descriptions of species 210 

Conclusions 219 

Description of a new species of fossil fish from the Esmeralda formation, 

by F. A Lucas 225 

21 GEOL, PT 2 13 193 



ILLUSTRATIONS. 



Page. 
Plate XXIV. Map showing the areal distribution of the Esmeralda formation. 198 
XXV. A, Contorted sandstones and shales at the coal mines; B, Lake 

beds east of Clayton Valley 200 

XX VI. Lake beds north of the Cave Spring road, at the west base of 

the Silver Peak Range 202 

XXVI I. Lake beds and overlying rhyolitic tuff on the south side of the 

white cone 3 miles northwest of Cave Spring 204 

XXVIII. Lacustral marls in ravine south of the Emigrant road at the 

east base of the Silver Peak Range 206 

XXIX. The Monocline, showing basalt capping pumice and lake beds. 208 
XXX. Plants from the Esmeralda formation: Glrirhrniti .', Dri/uji- 
terisf, SaMx, Cinchonidium?, Quercus, Rhus.', Spathyemaf, 

( 'hrysobalanus, ( 'ercis, and Mcus 222 

XXXI. Fossil fish from the Esmeralda formation ( Leuciscus turneri ). . . 224 
Fig. 5. Section of the Esmeralda formation 199 



THE ESMERALDA FORMATION, A FRESHWATER 
LAKE DEPOSIT. 



Bv H. W. Turner. 



GENERAL DESCRIPTION OF THE REGION. 

The deposits that have been designated the Esmeralda formation lie 
in the Silver Peak ' quadrangle in western Nevada, near the California 
line. The scenery is typical of the Great Basin, isolated ranges lying 
between broad valleys, many of which are of the nature of sinks. In 
the lowest part of most of the valleys are playas, and forming an inter- 
mediate zone between the playas and the ridges are detrital slopes, 
often of vast extent. The configuration of the country is in the main 
due to differential uplift and subsidence, and the valleys are thus 
chiefly of orographic origin.- Such a series of displacements must 
have been accompanied by normal faulting, and scarps originating in 
this way are to be seen in the region. In general the main faults trend 
north and south and east and west. Subsequent erosion has greatly 
modified the shapes of the ridges and partly tilled the valleys with 
detritus. 

In Middle Tertiary time much of the Silver Peak Range did not 
exist, and the remainder probably formed low ridges. Over a portion 
of its present site was a broad basin occupied by Lake Esmeralda. 
The deposits of this lake underlie the valleys and form foothill areas 
and arch up over the central part of the Silver Peak Range, showing 
these mountains to have originated in late Tertiary or post-Tertiary 
time. The deposits of Lake Esmeralda contain at some points an 
abundance of fossil fish and of dicotyledonous and other plants. The 
flora is represented by ferns, the fig, oak, willow, sumach, and soap- 
berry, and includes tree trunks t> to 8 feet in diameter, showing that 
the climate has undergone a great change since Tertiary time. From 
a well-watered region it has become an arid one in which there are no 
running streams. 

With the exception of certain gneisses of doubtful age, the oldest 
rocks of this district are sediments of Lower Cambrian age. the Middle 

I Ami. Geologist, March, 1900, Vol. XXV, p. 168. 

-Many of the sinks mid hike basins .'ire virtually rock basins surrounded by rucks older than the 
desert detritus. That sueli depressions could not lie formed by ordinary erosion seems clear. 

L97 



198 THE ESMEKALDA FORMATION. 

Cambrian and Silurian being- also represented. All of these Paleozoic- 
rocks are rich in fossils, which are often well preserved. 

Volcanic activity began in this region in early Paleozoic time. After 
these first flows of acid lavas the volcanic forces appear to have been 
quiescent for a very long period. During and subsequent to the deposi- 
tion of the lake beds, there were grout rhyolitic and andesitic erup- 
tions, followed probably in Pliocene time by eruptions of pumice and 
basalt. This disturbance continued into the Pleistocene, at one point 
building up a crater which still retains its original outlines. 

CHARACTER OF THE BEDS. 

The fresh-water deposits treated of in this paper may he designated 
the Esmeralda formation, the name being taken from the county in 
which they OCCUr. The he(l> are composed of sandstones, shales, and 
lacustral marls, with local developments of breccia and conglomerate 
on a large scale. The first published notice of these Tertiary lake beds 
appeai-s to he that of the mining engineer. Mr. M. A. Knapp, describing 
particularly the coal deposits 1 occurring in the beds at the north end 
of the Silver Peak Range. Mr. Knapp collected some molluscan 
remains near the coal beds, and these were examined by Dr. J. C 
Mciriam. of the University of California, who considered the shells 
indicative of fresh water, and possiblv Miocene in age. 

\i:i. LL DISTRIBUTION OF THE BEDS. 

On the accompanying areal map (PI. XXIV) of the central and 
northern parts of the Silver Peak quadrangle the distribution of the 
exposed portions of the Esmeralda formation is shown. In the south- 
ern part of the quadrangle the beds are visible at onlj a few points and 
undoubtedly are mostly wanting. There are older rocks at the surface 
nearly everywhere in the Palmetto Mountains and the southern part 
of the Silver Peak Range. The lake beds undoubtedly underlie 
the later deposits of Clayton Valley, of the southern pari of Big 
Smoky Valley, and of the northern part of Fish Lake Valley. They 
are also reported to have been struck in a well bored at Columbus, 
at the west side of the valley of that name, which lies just north of 
Silver Peak Range. It is probable that they underlie the Columbus 
Marsh. They certainly extend north of the Silver Peak quadrangle 
in Big Smoky Valley. As far as present evidence goes, within the 
limits of the Silver Peak region the basin containing Lake Esmeralda 
was bounded on the south by the Palmetto Mountains at the south end 

[•he coal fields of Esmeralda county, Nevada: Mining and Scientific Press, San Francisco, Vol. 
l.XXIV, 1897, p. 133. 

It might he noted, however, that fossil fishes from tin* formation wore- collected previously by J. E. 
ClaytonandW. P. Blake, but no description oi thesi fossils appears to bein print. Proc. California 
Acad. s,i.. Vol. Ill, 1866, p. 306. 



U. S. GEOLOGICAL SURREY 




Topography by W TGriSwold 



NORTH HALF OF S II ^ h. 

SHOWING AREAS OF T \i 



TWENTY-FIRST ANNUAL REPORT PART II PL. XXIV 




Geology by H. W Turner 



|||: SM E HALO A l-'l) K MAT ION 
:. i sMiles 



DISTRIBUTION AND THIOKNKSS. 



199 




THICKNKSS OF THE BEDS. 

No continuous section of the entire for- 
mation was found, but an attempt was 
made to estimate the approximate thick- 
ness of the beds. They dip nearly every- 
where at angles varying- from 5° to 60° 
from the horizontal and are broken by 
numerous small faults, so that often a 
layer followed along the strike is found 
to offset from lo to LOO feet or more 
every few hundred feet. However, in 
the section at the coal mine and in the 
zigzag section of the beds east of the 
south end of Big Smoky Valley, all of 
the sections being run at approximately 
right angles to the strike of the beds, no 
evidence of repetition by faulting or fold- 
ing was found, and the estimate may there- 
fore be taken as having an approximate 
value, subject to later revision when bet- 
ter sections of the format ion are found 
elsewhere. 

Section A -/>'. The base of t" 



of Clayton Valley, on the east by the Montezuma Mountains. an< 
the west by the Inyo Mountains, the north- 
ern limit being entirely unknown. More- 
over, this basin may easily have connected 
through the depression north of Lone 
Mountain with the Ralston Desert basin. 
which lies east of the Montezuma Moun- 
tains. The beds arch up over the central 
part of Silver Peak Range, reaching an 
altitude of 7,000 feet at Red Mountain. It 
is therefore clear that this portion of the 
range did not exist in Tertiary time, and 
that its site was a portion of the lake basin 
extending from the Inyo Mountains on the 
west to the Montezuma Mountains on the 
east. It is also clear that this portion of 
the range was uplifted in post-Esmeralda 
time. The highest part of the Silver Peak g 
Range attains an altitude of 9,500 feet, £, 
but the highest summits are made up of i 
Tertiarv lavas of later age than the lake ! 

beds. ' I 



\y 69 



ries appears to be the sandstone 



200 THE ESMERALDA FORMATION. 

shown in section A-B (PI. XXIV) across the Silver Peak Range through 
Red Mountain, on the east slope of which the sandstones attain a thick- 
ness of perhaps 2,000 feet. In a gulch three-fourths of a mile north of 
the summit of Red Mountain there are very abundant casts of a Unio 
which is specifically undeterminable. Lower down on the east slope 
are Carbonaceous shales which have been prospected for coal. Near 
these coal beds Mr. .1. lb Reed found some impressions of leaves of 
marsh plants and bones of fish. 

Section < I>. The Red Mountain series is presumably the same 
horizon as that in which the coal beds occur at the north base of the 
Silver Peak Range. Here section C-D was measured, and this section 
is assumed to represent the base of the formation in the Silver Peak 
region and to be .practically a repetition of A B. In this section the 
beds dip from 20 to b"> . usually to the east of north, the average dip 
being taken as •-'•'> . We have here a high ridge composed of ihyolite 
and rhyolitic tuff, the north face of which appeals to be a fauit scarp. 
as shown bj the displacement and contortion of the lake beds where 
they abut against it. and by the intrusion, along the line of faulting, 
of basaltic dikes. At some point- wot of the line of the section the 
lake bed- stand in a vertical position. Mr. Knapp, who figured a 
section to the we-t of (' 1). recognized the fault. lie states that the 
fault line lie- alone the north base of the range, dipping about 7."' N.. 
and that it -how- at the coal mine- a- a 30-foot cla\ gOUge between 
the volcanic rock- and the -hale-. PI. XXV. .1. represents the con- 
torted coal lied- near the fault zone we-t of the gulch in which the 
chief coal prospects aiv located. Fig. :, -how- graphically the sections 
described below: 

da formation. 

Section C-D, at the coal i »: .ln-t north of the rhyolite fault scarp Band- 
stones and shales, contorted or dipping irregularly 250 

Coal seam, immediately overlying which is a bed of shale containing i 
No. 92, mostly ferns. 

Sandstones and shales, w ith a layer containing very abundant fossil gas- 
teropoda (too 

Sandstone with seme- shale I, ion 

In this last horizon are contained the fossil leave- \... 89, together « ith - • 

Bhells an. I fish bones. The leal layers afforded most of the leave- described 
bj Professoi ECnowlton. There were also very abundant layers containing the 
remains of marshgrasses The section en<ls at the north edge of the quad- 
rangle, hm th«- l^ls continue t.. the northeast, toward the Monte Cristo 
Mountains. 

To the east of this section in the same area of the beds are -till higher beds, 
chiefly huff shales, and in one layer of these shales, which is purplish when 
freshly broken, very abundant and fairly well preserved fossil fish were found. 
The horizon in which they occur is presumed to be about the same as that 
in which similar though larger fish were found in section E-F, this hypothesis 
being based on the relative position of each fi-h layer above the massive sand- 



GEOLOGICAL SURVE 



WENTY-FIRST ANNUAL REPORT PART II PL. 




A. CONTORTED SANDSTONES AND SHALES AT THE COAL MINES. 




LAKE BEDS EAST OF CLAYTON VALLEY. 



turner.] SECTION OF THE FOKMATION. 201 

stone horizon which forms the top of section C-D and the base of the section 
E-F, and the sandstone horizon is used as a means of joining sections C-D 
and E-F. They thus overlap, but due allowance for this has been made in 
the measurements. Inasmuch as there is no visible connection between the 
sandstone horizon at D and at E, Big Smoky Valley lying between, the cor- 
rectness of the estimate of the thickness of the formation evidently depends 
on the same horizon being represented at these points. 

■■section E-F: The Bandstones, shales, and lacustral marls of the next part of 
the broken section here described do not contain fossil shells, leaves, or 
coal, so far as noted, and this lends support to the hypothesis here assumed, 
that all of the beds east of the south end of Big Smoky Valley are of later 
age than the beds containing the coal near the base of section C-D. In 
section E-F the beds dip 10° to 60° SE., the average dip being assumed to 
be 30°. 

Sandstone, shales, and lacustral marls 5, 200 

Deducting for o verlaj > on section C-D 1 , 000 

4, 200 

Above the massive basal sandstone of this section is a layer of rhyolitic 
pumice, perhaps 200 feet in thickness, and some andesite breccia. 

In the middle and upper portion of this series are remains of fishes over a 
foot long. The sandstones lying above the fish beds contain rhyolitic detritus, 
ami at this horizon are the fine white rhyolitic rocks in which the sulphur 
deposits noted later occur. 

Breccia beds with intercalated layers of sandstone 900 

Section F-G: The beds of this section dip to the east of south at from 40° to 
60°, the average dip being assumed to be 50°. 

Sandstones and shales 1 , 600 

Breccia beds 1, 300 

Sandstones and shales 1, 300 

At the top of this section is a layer of calcareous tufa in mammillary and 
thinolitic forms and a thin layer of conglomerate with well-rounded pebbles. 
Section II— I: At G the beds are displaced and the next section, H-I, is there- 
fore offset to a point to the southwest, beginning, as near as could be esti- 
mated, at the same beds as at G. The average dip of this section is 30° to 
the southeast. 

Sandstones and shales 800 

Breccia beds 1,000 

Lacustral marls 1,300 

At I there is supposed to be a line of faulting, for here is a bed of brown 
basaltic tuff with a nearly vertical dip, and the same bed of brown tuff may 
be noted on the north face of the Monocline, that lies about 2,000 feet south. 
The Monocline is presumed to be uplifted along this fault line, the present 
l>ositiun of the fault scarp to the south of the fault line being due to erosion, 
the basaltic cap preserving the scarp feature during its recession by protect- 
ing the soft underlying beds. The upper beds of this monocline may. there- 
fore, he taken as forming the top of the section. 

Monocline section 150 

In the section at the Monocline there is at the base white friable sandstone 
LOO feet, then brown tuff and white pumice 100 feet, and basalt 50 feet, 
but inasmuch as the brown tuff occurs at I, where there is supposed to be a 
line of faulting, the lower sandstone of the monocline is presumed to be 
included in section H-I, and is therefore omitted from the computation. So 



202 THE ESMEEALDA FORMATION. 

far as known there are no lake beds of the Esmeralda formation later in age 
than the basaltic flows represented by the basalt cap of the Monocline. The 
section may be said to end here. 

Total 14, 800 

The thickness of 14.800 feet of beds, as given in this estimate, seems 
incredible, although it may represent all of Miocene, and Pliocene 
time, inasmuch as. all the fossils that have any value in determining 
the age were found at the base of the formation. The held evidence 
of the occurrence of the basalt flows of the region, such as that capping 
the Monocline in Clayton Valley and supposed to represent the top of 
the section, certainly suggests for them a Pliocene age. for these basalt 
flows nearly everywhere cap mesas and seem to be the latest of the 
lavas, excepting only the basaltic eruptions that built up the finely 
preserved crater in Clayton Valley, which is clearly of Pleistocene age. 

The depth below the surface of the 1 basement complex on which the 
beds rest, and the angle at which the lake beds rest on this complex, 
are of course entirely unknown. In all probability the rocks underlying 
section C-D are vertical slates and cherts of the Palmetto formation 
(Lower Silurian), since these beds outcrop not far to the west. 

DETAILS OF THE SECTIONS. 

The calcareous tufa found at G strongly resembles similar deposits 
found by Professor Russell and others in the Lake Lahontan beds on 
the shores of Mono Lake. The thickness of the tufa is perhaps 20 
feet, and it was not observed elsewhere in the beds. A specimen of 
the prismatic form of the tufa or thinolite was sent to Prof. E. S. 
Dana, who was struck with its resemblance to the thinolite of Lake 
Lahontan. Professor Dana suggests that the original material may 
have been crystallized aragonite. which has gone over to calcite by 
paramorphism, regarding this as a more probable origin than that 
which he formerly suggested, 1 thai thinolite is a pseudomorph after a 
double salt of calcium and sodium. To the south of the road, about 
three-fourths of a mile west of Cave Spring, is a streak of travertine 
along the base of a low ridge of tawny sandstone. This appeal's, 
however, to be a spring deposit (possibly formed at the same time as 
the sandstone) and. therefore, of a different nature from the tufa depos- 
its formed from the lake waters. Similar travertine deposits were 
observed elsewhere, sometimes near or in the lake beds, but some of 
these are probably of recent origin. 

Any one looking at the low hills that lie east and southeast of the 
south end of Big Smoky Valley will see bare yellow sandstone, hills 
and a large group of low hills and ridges of a dark color. He may at 
once draw the conclusion that the two sets of hills are composed of 

'Bull. U. S. Gcol. survey No. 12, 1884, p. 25. 



turner.] AGE OK THE LAKE BEDS. 203 

different materials, probably of different ages. A cursory examina- 
tion of the dark hills would strengthen this conclusion, for they arc 
covered with loose fragments of all the Cambrian and Silurian rocks 
that comprise the higher ridges to the east. A more careful exami- 
nation, however, discloses the fact that underneath this loose material 
there are massive-bedded breccias with thin sandstone layers interca- 
lated, and that this entire scries dips conformably with the sandstones 
of the yellow areas — that is, to the south and southeast. Frequently 
any one layer of this breccia is composed chiefly of one kind of Paleozoic 
rock; thus some layers outcrop as reefs of limestone, identical in gen- 
eral appearance to similar reefs in the Paleozoic terranes; other 
layers are composed chiefly of green Cambrian slate; so that if the 
broken-up nature of the material were not evident and these reefs were 
not intercalated with layers of Tertiary sandstone, one might easily, 
on a cursory inspection, suppose that he had to do with deposits of 
Paleozoic age. These breccias evidently represent old detrital slopes 
of Tertiary age, and seem to indicate an uplift or a drier period in the 
formation of the lake beds, followed again by a depression, as indi- 
cated by the tine sediments overlying. 

East of the Clayton Valley playa lacustral marls only appear to 
have been laid down — at least only these upper beds are exposed. 
They are capped with rhyolitic sandstone, the entire series dipping 
from 5° to 10° SE. These beds are shown on PI. XXV, B. 

A short but interesting section of the lake beds is to be seen in the 
wide, steep-sided ravine south of the Emigrant road at the east base of 
the Silver Peak Range. The lake beds abut abruptly against a wall 
of rhyolite on the west, and this rhyolite appears to have forced its 
way up at this point, but it is possible that the contact is one due to 
faulting. The beds nearest the rhyolite are tern-gray lacustral marls, 
which weather into softly rounded knolls, some of which are represented 
on PI. XXVIII. There is a layer of andesite breccia and one of rhy- 
olitic pumice interbedded in the marls. The breccia contains abundant 
fragments of silicified wood. Exactly the position in the series that 
this section occupies was not determined, but the rhyolitic pumice 
layer may easily be the same as that near the base of section E-F, 
there being in both cases andesitic breccia near by. 

ACxE OF THE LAKE BEDS. 

The fossil shells, consisting chiefly of gasteropods from near the 
coal mines, are in about the same horizon as the leaves, and presum- 
ably also in about the same horizon as the fresh-water clams ( Unio) col- 
lected north of lied Mountain. All of the fossil shells were referred 
to Dr. J. C. Merriam, of Berkeley, California, who states: 

I find four species of shells in your collection, Campeloma sp., Unio sp., Planorbis 
Yiki-.ynrhihilisyiwk, and A ncylus like undulatus Meek. The first three forms resemble 



204 THE ESMERALDA FORMATION. 

species described from the Eocene of western United States; the last form resem- 
bles a species described from supposed Miocene beds. Though I do not regard 
these few forms as characteristic enough to determine the age of the beds definitely, 
I should think they mighl be early Miocene or late Eocene. 

Mr. J. E. Spurr collected some poorly preserved shells from the 
Esmeralda formation about L0 miles southeast of Columbus. These 
were referred to Dr. W. II. Dall, who was unable to identify any of 
them with certainty. He found a bivalve that may be a Sphserium, 
and a gasteropod that may be a Planorbis. Dr. Dall thought the 
forms suggested a fresh-water origin. 

According to Clarence King 1 Anq/lns undulatus Meek and two 
species of SphcBrium are f ound in the Truckee beds in the Kawsoh 
Mountains of Nevada, in the fortieth parallel region. The Truckee 
beds are supposed to be of the same age as the John Day beds of 
Oregon, and King refers the Truckee group to the Miocene, chiefly 
on the basis of the vertebrate remains found in the John Day beds. 
Later investigations may therefore correlate the Esmeralda forma- 
tion with the Truckee beds of Pah Ute Lake. Moreover, the John 

Day beds are said to antedate the basiltic eruptions, and this is like- 
wise the case with the Esmeralda deposits. The collection of fossil 
fish was obtained chiefly from a single layer in the buff shales. 3.V 
miles due easl of the coal mines. It comprises a large number of 
individuals, many of them fairly well preserved. Prof. F. A. Lucas. 
of the United States National Museum, regards them all as forms of 
one species of Leuciscus, not differing greatly from living forms. 

The fossil leaves were referred to Prof. V. 11. Knowlton. Being 
mostly new species 1 1 n • \ are <>f little value in determining age, but 
from the resemblance of many of them to living forms Professor 
Knowlton regards them as of a comparativelj recent age. One 
species. Salix angmta, is found in the Green River group (Eocene). 
Another species, a Cinchonidium, is allied to a form in the Fort Union 
group( Eocene '.). The fossil lid>. v\ hich, according to Professor Lucas, 
resembles a modern form, presumably suggests a Pliocene rather than 
a Miocene age, but being also a new species, like most of the fossil 
leaves, it is of little value for present purposes in determining age, 
although valuable for future correlation. 

The evidence of the age of the beds as obtained from paleontologic 
data is thus unsatisfaetoiy, but the resemblance of some species of 
both mollusks and plants to Eocene forms and the resemblance of 
several of the plaids and of the tish to living forms suggest a Middle 
Tertiary or Miocene age for the fossil-bearing horizons, yet inasmuch 
as the fossils come chiefly from near the base of the formation it 
seems quite probable that the upper beds are of Pliocene age, so that 
the formation as a whole should be designated Neocene. What may 

i U.S.Geol.Expl i urti th Par., Vol. I, p. 422. 



turner.] RELATION OF LAKE BEDS TO LAVAS. 205 

be regarded as additional evidence of the Miocene age of the basal beds 
of the series is the indurated character of the sandstones in the ravines 
north and south of the Cave Spring road on the west side of the Sil- 
ver Peak Range, and the character of the coal at the base of section 
C-D. This coal contains more fixed carbon than volatile hydro- 
carbons, while in the coals of the Tejon formation (Eocene) of Cali- 
fornia, the volatile hydrocarbons are in excess of the fixed carbon. 
Since, other things being equal, the older a coal the more fixed carbon 
it contains, the inference is drawn that these coals are at least pre- 
Pliocene. This last inference is, however, of doubtful value, inas- 
much as in certain instances the same bed has appeared as lignite 
at one point and as bituminous coal at another. 



REEATIOX of the lake beds to the lavas of the 

REGION. 

What may be regarded as the oldest lavas associated with the lake 
beds are narrow dikes and thin intruded sheets of andesite, usually 
much altered, in the hardened sandstones of the gulches south of the 
Cave Spring road at the west base of the Silver Peak Range. This 
inference is drawn from the altered character of the intrusions, the 
date of the intrusions being unknown. At the locality near the coal 
mines, where leaves No. 92 were collected, is a light-gray volcanic 
layer, rich in biotite, and this layer is interstratified with shale. This 
clearly indicates an eruption of the age of the inclosing beds. The 
lava contains numerous crystals, broken or entire, of plagioclase, 
sanidine, quartz, and biotite, in a groundmass that appears to be a 
devitrified glass. From the abundance of the plagioclase and biotite, 
and from the fact that the groundmass has an index of refraction 
greater than that of balsam, and hence is somewhat basic, this material 
may be called a dacite. 

To the south of the Cave Spring road on the west side of the Silver 
Peak Range are extensive beds of sandstone and conglomerate, the lat- 
ter containing abundant pebbles and fragments of rhyolite and of the 
coarse andesite that caps the neighboring ridges. In this volcanic 
conglomerate at one point is an intruded sheet of olivine-basalt. 
Since the basal sandstones here clearly underlie the rhyolites and 
andesites, it is evident that these conglomerates represent a much 
later time than do the basal sandstones. Between the period of the 
deposition of the basal sandstones and the associated conglomerates 
and the formation of the later conglomerates above noted the main 
rhyolite and andesite eruptions took place. Nevertheless, there were 
earlier rhyolitic and andesitic eruptions, as is evidenced by the well- 
rounded pebbles of these rocks in the conglomerates associated with 
the basal sandstones. Some of these earlier conglomerate beds dis- 



206 THE ESMERALDA FORMATION. 

tinctly underlie the massive rhyolite tuffs; for example, those foi-m- 
ing the white cone having an altitude of 7,100 feet, 3 miles northwest 
ot Lave Spring, a view of which is presented on PI. XXVII. 

South of the Emigrant road, as already noted, there is a layer of 
andesite breccia in the lake beds containing fossil wood, and overlying 
it, perhaps 200 feet, is a layer of rhyolitic pumice. This section is 
probably higher up than section C-D, which contains the dacite, and 
very likely, as before indicated, represents the basal part of section 
E-F. To the east of Big Smoky Valley, and to the north of the zig- 
zag section E-F-G-H-I, still higher in the series, are extensive beds 
of conglomerate with well-rounded pebbles. In these conglomerates 
are layers of while pumice. Finally, we have at the monocline and 
at other points rhyolitic tuffs and pumice capped by basalt. Very 
probably the brown tuff in the Monocline is of basaltic origin, but at 

numerous other point-, especially southwest of Silver Peak, there are 
e\ten-'\ e beds of rhyolitic pumice and tuff overlying lake beds and 
capped by basalt. There is also ;it the Monocline a layer of white 
pumice between the brown tuff and the basalt cap. The basaltic erup- 
tions are regarded as the closing event in the history of the deposition 
of the sediment- of Lake Esmeralda. 

VEIN DEPOSITS OF THE FORMATION. 

In the sandstone- exposed in the ravine- north and south of the 
Cave Spring road on the west side of the Silver Peak Range and in 

the -and-ti s of the area in which the coal mines occur are frequent 

white veins following in most cases fault lines. In some instances 

these contain fragments of the wall rock-. These veins are made up 

chiefly of calcite, sometimes in part of chalcedony, and some of them 

contain green coloring matter, apparently of a chloritic nature. The 
veins dip from 30 to 90 from horizontal it y and are from half an inch 
to 2 feet in thickness. 



KcoxoMir in:iM)sir» <>i rm: formation. 



The chief material of economic value in the lake beds IS coal, which 
form- one or more layers in the sandstone at the north base of the 
Silver Peak Range. This has been opened by inclines at several 
points. According to Knapp there are two -cams, one li feet and 
the other ."> feet thick. I [e supposes these beds to extend north under 
Columbus Valley, which i- highly probable. They should, however, 
be found much nearer the surface in the low divide separating 
Columbus and Big Smoky valleys, where at some points the dip of 
the strata is only 5°. The coal prospects examined by Knapp were 



ECONOMIC DEPOSITS IN THE EORMATION. 



207 



probably those near the head of the gulch in which most of the work- 
ings lie, and these are near the zone of faulting previously referred to. 
The inclines being worked at the time of the writer's visit (1899) are 
farther north, where the thickness of the single layer of coal is 10 feet, 
the dip being 20° to 30° NE. This coal may be designated lignite. 
From the analyses given below it will be noted that when burned it 
leaves a large amount of ash. This is said to be the chief objection 
raised against it by the engineers of the Central Pacific Railroad, who 
made a locomotive test. 



Analyses of coal from the Esmeralda form 


< it ion. 






Elder-Mor- 
gan mine, a 


Knapp's 
average. 




Per cent 
3.53 
31. 71 

35. 95 

28.81 


Per cent. 

| 31.5 

38.5 
30 






Ash . . 




100. 00 
1.05 


100 





aDr. Hillebrand notes that the i 
but not much swelled. 



ightgray and containssomesulphiite. The coke is coherent, 



The first analysis, by Dr. W. F. Hillebrand. was made in the chem- 
ical laboratory of the United States Geological Survey, the coal being 
a sample from the Elder-Morgan mine. The second analysis is that 
given by Knapp as the average anal} r sis. 

While it is probable that this coal will be of local value for stationary 
engines, house use, etc., it is not likely to be used on the railroads on 
account of the high percentage of ash, requiring the frequent cleaning 
of the ash boxes. It is said to be a good coking coal, but its value in 
this respect, so far as the writer is aware, has not been determined by 
a practical test. The chief difficulty in mining it at present is that for 
the larger part of the year there is no drinking water near the mines 
and no timber. Since the layers probably underlie the district north 
and northeast of the outcrops at the mines, the quantity of coal availa- 
ble is very likely large. 



SULPHUR. 



To the east of the south end of Big Smoky Valley, in a fine-grained, 
white, decomposed material, perhaps a rhyolitic tuff or silt, is a deposit 
of sulphur, which was at one time worked. The locality is just east 
of the Reese River road. -2 miles north of bench mark 4996. The 



208 THE ESMERALDA FORMATION. 

white rock is intersected by fractures and joints, and the sulphur 
seems to have come up as vapor from below and to have been deposited 
by sublimation in the fractures. Most of the sulphur is yellow, and 
much of it shows crystal faces. There is also an efflorescence of 
alum in seams of the rock in the old cuts. Another sulphur prospect 
lies just northeast, across the gulch. Here some sulphur crystals are 
an inch in diameter. 



FOSSIL PLANTS OF THE ESMERALDA FORMATION. 



Bv F. H. Knowlton. 



INTRODUCTION. 

In July. L899, Mr. H. W. Turner, of the United States Geological 

Survey, sent me a small box containing a few fossil leaves collected 
near Silver Peak. Esmeralda County, Nevada. A hasty examination 
showed much of interest, and Mr. Turner was requested to secure as 
large a collection as possible from the locality. Later in the season 
he sent in an additional box of material, which has furnished the basis 
for t he following report. 

The beds containing these plants, to which Mr. Turner has given 
the name Esmeralda formation. ' occur at the northern end of the 
Silver Peak Range, in Esmeralda County, Nevada. They consist of 
sandstones and shales having an approximate thickness of 2,000 feet, 
and were laid down in pari at least in fresh-water lakes. These beds 
contain extensive deposits of coal, and the fossil remains occur in close 
proximity to the coal seams and embrace, besides the plants, a few 
fresh-water shells and fish remains. The shells have been studied by 
Dr. J. ( '. Merriam, and the tish remains by Mr. F. A. Lucas, of the 
United States National Museum, whose report follows this. 

The exact localities for the fossil plants are as follows: 

Number 92: Immediately overlying a LO-fool coal seam. 3.8 km. 
northeast of Emigrant Peak, at the northern base of the Silver Peak 
Range, Esmeralda County, Nevada. 

Number 89: Sandy shale 4.5 km. northeast of Emigrant Peak, at the 
northern base of the Silver Peak Range, Esmeralda County, Nevada. 

This series overlies No. 92. 

At Mr. Turner's request I made a very hasty preliminary examina- 
tion of this collection and prepared a brief report, a portion of which 
was printed in the paper cited. At that time 1 mentioned the 
presence of two previously known forms, viz. Rhus fraterna Lx., 
and Ilex quereifolia Lx., bul a careful examination has convinced me 



■ Am. (ipologist, March L900 ' 
21 GEOL, I "I' 2 14 



210 FOSSIL PLANTS OF THE ESMERALDA FORMATION. 

that, while close to these species, the forms in question are sufficiently 
distinct to warrant their being described us new to science. While 
the plants of this little collection have in general a familiar facies, 
they are found to differ in a greater or less degree from described 
forms and consequently have been regarded as new. This florula, as 
at present constituted, embraces 14- forms, which are described below. 

DESCRIPTIONS OF SPECIES. 

( .i.i.Miir.M \ '. OB8CHRA n. sp. 
I'l. \X\, figs. 1-4.) 

Outline of frond unknown; pinna' linear -lanceolate in shape, cut 
nearly or quite to the rachis into alternate or opposite, deltoid, acute, 
slightly scythe-shaped entire segments; nervation obscure, but with a 
midvein which is near the lower margin and few apparently once- 
forking very slender vein--, fructification unknown. 

This interesting form is represented in the collection by a consider- 
able number of fragments. It is impossible tomakeoul the original form 
of the frond, a^ none bul detached fragments of pinna' are found, but 
it was probably a compound frond. The pinnae are narrowly lanceo- 
late, the Longest frag nts preserved being only aboul 2 cm. in length. 

The width varies from •"» to s mm. Neither base nor apex is presen ed. 
As stated in the diagnosis, the nervation is obscure, but it consists of 
a thin midvein, which is located much nearer the Lower margin, and 
of a few apparently once-forking veins. While the fructification is 
not preserved, there is some slight indication that it consisted of a few 
minute sori on cither side of the midvein and about midway between 
it and the margin, but this is too obscure to be of value. 

I have hesitated to describe this form, as the material is so very 
fragmentary that its size and relationship can not be made, out with 
any thing like satisfaction, and especially have I hesitated to refer it to 
Gleichenia. It. however, agrees so exactly in size and shape with G. 

polypodioides Sm., of the Cape of Good Hope, that it seems unwise 

to separate them generically. The nerves in the living species are not 
forked, while in the fossil tiny seem to lie once forked; but this is 
obscure. 

This form is also much like a number of other living ferns, as. for 
instance. Pol/ypodium verrulatum Mett., a species living in the Antilles, 
Mexico, and South America. It is, however, closer to the species of 
Gl< ill,, nil/ above mentioned, and I have tentatively referred it to this 
genus. It lacks the characteristic branching usually observed in the 
fronds of this genus and may not belong to it. 

Locality: Northern base of Silver Peak Range. 3.8 km. northeast of 
Emigrant Peak. 



knowlton.] DESCRIPTIONS OF SPECIES. 211 

DbYOPTEEIS? GLEICHENOIDES 1). sp. 
(EL XXX, figs. 5-7. ) 

Outline of frond unknown; pinnse lanceolate-deltoid in outline, cut 
to about one-half the distance to the rachis into ovate, obtuse, entire. 
slightly scythe-shaped segments; midvein thin, in the middle of each 
segment or pinnule; lateral veins about 5 pairs in each pinnule, each 
once forked in the middle; fruit unknown. 

The collection contains a large number of fragments that appear to 
belong to this form. They appear to be pinna? from a large frond, 
but there are none connected and hence there is no indication of the 
size and shape of the frond as a whole. The fragments preserved are 
about 2 to 2.5 cm. in length and about 1 cm. in width. They are well 
shown in the drawings. 

I am very uncertain as to the proper generic reference of this form, 
as there is no trace of fruit preserved. It is found not only in the same 
beds as the last-mentioned form, but often preserved on the same 
pieces of matrix, and was at first supposed to represent a variation of 
it, but after a careful examination I am not certain of this. Both of 
the forms appear to vary considerably, yet they do not actually seem 
to join, and I have kept them separate, even generically. 

Locality: Northern base of Silver Peak Range, 3.8 km. northeast of 
Emigrant Peak. 

SPATHYEMA % NEVADENSIS 11. sp. 

(PI. XXX, figs. 17, 18.) 

Spadix globose or oblong ; perianth succulent, circular, or by compres- 
sion elliptical or irregularly quadrangular in shape; ovary immersed, 
leaving a deep pit. 

I am very uncertain as to the fossil here described and figured. It 
appears to have been a globose or club-shaped spadix with numerous 
ovaries immersed in thickened portions of its substance. Each ovary 
now appears as a pit sunk in flesh}' segments of the spadix, which are 
elliptical, nearly circular, or irregularly quadrangular in shape and 
apparently surrounded by a thicker rim or wall. The upper or outer 
surface of each is minutely papillose or roughened. These thickened 
portions vary much in size, the smallest being hardly more than 1 mm. 
in diameter, while the largest are fully 8 mm. across. This difference 
in size is perhaps due to their being in different stages of development. 

This curious organism was at first supposed to belong to the animal 
kingdom, but it has been shown to a number of zoologists, and all are 
positive it can not be of an animal nature. It was then shown to 
several botanists, and the conclusion was reached that it was an aroid 



212 FOSSIL PLANTS OF THE ESMERALDA FORMATION. 

spadix. When compared with the spadix of 8pathy< ma ( Symplocarpus) 

firt'nlii. it is seen that there are numerous points in common, and. while 
it does not agree in every particular, it is certainly very suggestive of 
this, and 1 have ventured so to place it. It is associated on the matrix 
with fragments of sedge-like plants, which would seem to indicate that 
i( was a denizen of moist or swamp\ localities, such as Spathyema is 
known to delight in. More and better material will be necessary 
before it- exact status call lie Settled. 

Locality: Northern base of Silver Teak Range, 3.8 km. northeast of 
Emigrant Peak. 

Unknown plant. 
(Hate \W. fige. 16,24,25.) 

The collation contains a number of \er\ curious plants, three of 
the besl of which are here figured. They are associated on the same 
pieces of matrix as the form described under the name Spathyema f 
n, r, hI, //.v/.v. ami may have 90me connection with that species; yet the 
connection, if such there lie. i- ver\ obscure, and can not he made out 
w ith certainty. 

They have the appearance of being some sort of a fructification 
inclosed on all sides bj a thin, membranous covering. In shape thej 
are elliptical or elliptical-oblong. The smallest is about 1*; mm. long 
and In mm. wide, while the central, apparently fruiting portion is 10 
mm. long and about 7 mm. wide. The largest specimen i- 22 mm. long 
and L8 mm. wide. The other specimens approach in size the first one 
mentioned ahoy e. 

Local it} : Northern base of Silver Peak Range, 3.8 km. northeast of 
Emigranl Peak. 

Salu w.i si \ ' Al. Br. 

The collection conta!.. • a single fragment, together with its counter- 
part, which seems to belong to this species. It is nothing more than 
a segmenl out of the middle of a narrowly lanceolate leaf, and has 

the same nervation a- that shown by Lesquereux for the American 
leaves referred to this form. 

Locality: Northern base of the Silver Peak Range, t.5 km. north- 
east of Emigrant Peak. 

Saijx \ \< i imi i n.i \ n. sp. 

PI. XXX. figs, v 20. 

Leaves -mall, subcoriaceous in texture, lanceolate in outline, about 

equally narrowed to both base and apex: margin perfectly entile; 

petiole short, -tout: midrib strong below, becoming much thinner 



knowlton.] DESCRIPTIONS OF SPECIES. 213 

above; secondaries numerous, close, alternate or subopposite, at an 

aiielc of about 50 c , apparently camptodrome; finer nervation not 
preserved. 

'Phis little species is represented by several more or less perfect 
leaves, two of the best of which are here figured. It is lanceolate- 
acuminate in shape, about 2.5 to 5.5 cm. in length and 6 to 13 mm. in 
width. The petiole is only about 2 mm. in length. 

This species appears to be quite closely allied to the living Salix 
■fktmatilis Nutt. (S. longifolia Muhl.), a species abundant throughout 
most of the region west of the Mississippi. It is not, however, like 
what may be called the typical form, with long narrow leaves, but is 
similar to certain of the smaller, relatively broader-leaved forms. It 
does not appear to approach very closely to any previously described 
fossil North American species. 

Locality: Northern base of Silver Peak Range, 3.8 and 1.5 km. north- 
east of Emigrant Peak. 

Salix sp. 

(PL XXX, fig. 13.) 

Leaves of firm texture, narrowly lanceolate in shape, base destroyed, 
apex apparently long-acuminate; margin obscurely serrate above; mid- 
rib rather slender; secondaries few, alternate, at an acute angle, much 
arching upward, running along near the margin for a considerable 
distance, apparently sending weak branches on the outside to the mar- 
ginal teeth; finer nervation obscure, apparently broken. 

This form is represented by the single broken example figured, 
which lacks both base and apex. It is narrowly lanceolate, the por- 
tion preserved being about 7 cm. in length and 13 mm. in width at the 
broadest point, which is apparently about the middle of the leaf. The 
full length when perfect was probably about 9 or 10 cm. 

While this species is clearly a Salix and allied to a number of de- 
scribed forms, I have hesitated to name it on this scanty material. It 
has much the shape and size of Salix angusta Al. Br., 1 but appears to 
differ in being obscurely toothed above. The teeth, however, are to 
be made out with difficulty, and as then 1 is only one specimen, together 
with its counterpart, it seems best not to give it a name. 

Locality: Northern base of Silver Peak Range, 1.5 km. northeast of 
Emigrant Peak. 

Salix \ sp. 

(PI. XXX, fig. 14.) 

Leaves of firm texture, elliptical-lanceolate in outline, about equally 
narrowed to both base and apex; petiole long, rather strong for the 



214 FOSSIL PLANTS OF THE ESMERALDA FORMATION. 

size of the blade; margin perfectly entire- midrib moderately strong; 
secondaries thin, about 7 or 8 pairs, alternate, at an angle of about 
45 . very slightly arching upward; remainder of nervation obsolete 1 . 

The collection contains several leaves that appear to be identical, one 
of the best of which is figured. They are well preserved as regards 
outline, but the nervation is nearly obsolete. These Leaves are rather 
broadly lanceolate in outline, being I to 4.5 cm. iii lengthand 11 to 13 
mm. in width. The petiole preserved in only one instance is about 1 
cm. long. 

These leaves appear to belong to Salix, but the finer nervation is so 
obscure that it i- Impossible to determine them with satisfaction. 1 
have therefore placed them under Salix, but have not attempted to 
point out relationships. 

Locality: Northern base of the Silver Peak Range, 3.8 km. northeast 
of Emigrant Peak. 

QUERCUS TURNER] D. -p. 
PL \W. fig. 21.) 
Leaf evidently thick and coriaceous, elongated, elliptical in general 
outline, truncate and oblique at base, obtuse at ape\; margin provided 

with numerous large rather obtuse teeth, separated by shallow, mainly 
rounded sinuses; petiole slender; midrib slender; secondaries about 
12 pairs, -lender. Irregular, both opposite and alternate, emerging al 
various but mostly at low angle-, passing to the marginal teeth, occa- 
sionally forking and the branches entering the teeth; nervilles numer- 
ous, all broken: liner nen at ion Conning numerous quadrangular areas. 

This species is represented by the example figured and its counter- 
part and several smaller fragments. It is narrowly elliptical in out- 
line, being about t.5 cm. long and 2 cm. wide in the middle. The base 
is truncate or square on one side and oblique or wedge-shaped on the 
other, while the apex is quite obtuse. The margin is provided with 
numerous large l"\\ teeth, which .ire separated by -hallow sinuses. 
The nervation is beautifully preserved, consisting of a rather -lender 
midrib and about \-2 pairs of irregular secondaries and numerous 
broken nervilles. The finer nervation form- numerous rather large 
irregularly quadrangular areas. 

This specie- i- rather closely allied to certain living and fossil form.-. 
Thus it is similar in shape to Qm reus undndata Torrey, a species found 
in the southern Rocky Mountain region, but differs in being much 
larger and in having a larger number of secondaries. It is also similar 
toQ. dumosa polycwrpa Cxn ene, but is perhaps nearest toQ. turbindla 
Greene, a shrubby specie- ,,i southern California and Arizona, on the 
borders of the Mohave Desert. The leaves of the latter are much 
-mailer than the one under consideration and have a smaller number of 
teeth and secondaries, but the liner nervation is the same. 



knowlton.] DESCRIPTIONS OF SPECIES. 215 

Among fossil species it is very near to Quercus (tpphijul* ! Kn., 1 
from the Miocene of the Cascade Range found near Ashland, Oregon. 
This differs in being less truncate at base and much more acuminate at 
apex, and has the more rounded teeth. The finer nervation is similar, 
but not quite so much broken up. 

Locality: Northern base of the Silver Peak Range, 4.5 km. northeast 
of Emigrant Peak. 

QlJERCUS ARGENTUM n. sp. 

(PI. XXX, fig. 12.) 

Leaf of firm texture, lanceolate in outline, undulate margined and 
about equally narrowed at both base and apex; petiole short, slender; 
midrib slender; secondaries about 8 pairs, at irregular distances, 
alternate, emerging at an angle of about 45°, thin, camptodrome, 
arching near the margin; nervilles rather few, broken; finer nervation 
producing larger, irregularly quadrangular areas. 

This little leaf, the only one found, is lanceolate with irregularly 
undulate margins. As preserved it is 4.25 cm. in length exclusive of 
the petiole, which is 6 mm. long. The nervation consists of about 8 
pairs of alternate, irregular secondaries and a loosely areolated liner 
network, which is unmistakably que'rcoid in appearance. 

This species does not appear to be very closely related to any species 
either living or fossil with which I am familiar, yet it seems undoubt- 
edly to belong to Quercus, and I have so placed it. 

Locality: Northern base of the Silver Peak Range, 4.5 km. north- 
east of Emigrant Peak. 

Ficus j,acusttus n. sp. 
(PI. XXX, fig. 26.) 

Leaves thick and coriaceous, apparently elliptical in general outline, 
rounded and very unequal-sided at base (apex destroyed); margin 
entire; petiole short, very thick; midrib thick, straight; secondaries 
numerous, alternate, very thin and deeply concealed in the parenchyma, 
slightly flexuose, the lowest pair arising at the base of the blade, and 
the one on the broad side of the blade with numerous outside blanches 
which arch just inside the margin and join by broad loops; other sec- 
ondaries with few outside branches which loop in the same manner; 
nerviHes numerous, irregular, and mainly broken; finer nervation pro- 
ducing irregularly quadrangular areola'. 

The example figured is all that was found of this species and unfor- 
tunately this lacks the upper portion. The part preserved is about 
<) cm. in length, and was possibly as much longer when living. The 
widest point is a little more than 4 cm., although it is so unequal-sided 

1 Twentieth Aim. Rept. D. S. Geo!. Survey, Part in. p. -12. Pl.I,flgs.6,7. 



216 FOSSIL PLANTS OF THE ESMERALDA FORMATION. 

that it is not possible to judge accurately of it. The petiole is thick, 
being- 3 mm. in width. The length preserved is 1.5 cm. but in all prob- 
ability this is not the whole of it. 

Locality: Northern base of the Silver Peak Range. 1.5 km. north- 
east of Emigrant Peak. 

ChRYSOBALANUS l'oi.r.AKIH.VNA n. sp. 

(l'l. XXX, Bg. 19. i 

Lent' coriaceous ill texture, broadly elliptical in outline, slightly 
heart-shaped at base, rounded and obtuse at apex: petiole short, thick; 
midrib very thick below, becoming much thinner above; secondaries 
about L2 pair-, alternate, irregular, very thin, emerging at a low, 
almost right angle, camptodrome, arching well inside the margin and 
joining the one next above, with a series of small loops outside; 
nervines very thin, all broken; finer nervation forming very numerous 
irregularly quadrangular area-. 

The example figured is the only one contained in the collection. It 
is nearly perfect, lacking only a small portion of one side. It is broad- 
elliptical in shape, being about ■> cm. in length and I cm. in width. 
Tli. petiole is only 2 or :'. mm. in length, although it was possibly a 
little longer when living. This leaf was clearly very thick and cori- 
aceous and has a very thick midrib, which, however, becomes much 
thinner above the middle. The secondaries are very thin and nearly 
at right angles to the midrib, arching some distance inside the margin 

and passing to tin e next above by a series of loops. The finer 

nervation is beautifully preserved, forming rather large irregularly 
quadrangular area-. 

I have been sonievv hat in doubt as to the proper generic reference of 
this finely preserved leaf. At first glance it seems to belong to Ficus, 
being similar in nervation to a number that have been so regarded. It 
has also considerable resemblan< e to certain of the larger-leaved species 
of Arctostaphylos, so abundant on the Pacificcoast; but while the shape 
and coriaceous character are the same, the secondaries in all species I 
have been aide to see are at an acute angle of divergence. The leaf 
before u- seems to agree quite closely with the genus Ohrysdbalanus^ 
and I have SO considered it. The only species of this genus now living 
in the United State- i- ( . icaco I-., which is confined to southern Flor- 
ida. This species is also widely distributed in the West Indies. .Mexico. 
and ( 'entral America. 

I take pleasure in naming tin- fossil species in honor of Mr. 
Charles Louis Pollard, of the United State- National Museum, who 
suggested it- probable relationship to Chrysobalanus. 

Locality: Northern base of the Silver Peak Range, 1.5 km. north- 
east of Emigrant Peak. 



Kxmvi.TON-.j DESCRIPTIONS OF SPECIES. 217 

CeRCIS I NEVADENSIS 11. Sp. 
(PL XXX, fig. 23.) 

Loaf membranous, outline uncertain but apparently circular or 
approximately so, regularly rounded at base; margin entire; petiole 
very long and slender; nervation palmately five-ribbed from the apex 
of the petiole; midrib slightly strongest, with a number of alternate 
branches in the upper part; lateral ribs slightly weaker, the inner 
with four or five branches on the outside, all camptodrome and arch- 
ing just inside the margin; lowest pair of ribs with a few loops on the 
lower side; nervilles few, irregular, and much broken; finer nerva- 
tion producing large irregular areas. 

The fragment figured is practically all of this form in the collection. 
As may be seen by the figure, it represents only the lower portion of 
the blade. The outline can not be determined, although it seems to 
have been approximately circular. The base is regularly rounded and 
the margin perfectly entire. The petiole was very long and slender 
for the apparent size of the leaf, being 2.75 cm. in length and evi- 
dently not all preserved. The nervation is well shown in the figure, 
being palmately five-ribbed. 

The specimen is so fragmentary that it is quite impossible to make 
out all the characters, } T et, as far as can be noted, it seems to approach 
closest to Cerch. This genus at present embraces about five species, 
Datives of North America, Europe, and temperate Asia. In all the 
living species the base of the leaves is much more heart-shaped than 
is the fossil under consideration, and usually there are seven ribs. 
Occasionally, however, leaves may be found that have only five ribs 
and the blade somewhat less heart-shaped. This is especially the case 
with ( '. chinensis and occasionally in leaves of C. occidental 7s. Nut t., 
from the Pacific coast. The disposition of the ribs and their secondary 
branches is practically identical in both living and the present fossil 
species. 

Thus far three fossil species of Gereis have been described from this 
country, as follows: G. parvifolia Lx., 1 from Florissant, Colorado; 
('. truncata Lx. , 2 from the Bad Lands of Dakota, and C. horeaUs 
Newb., 8 from the Fort Union beds near the mouth of the Yellowstone 
River, Montana. Our leaf seems to be very close indeed to C. parvi- 
folia, but differs in being much larger and in having a much longer, 
more slender petiole. Gereis truncata has never been figured, but it 
is described as exactly similar in form and nervation to the preced- 
ing species, differing only in being very much larger and more pointed. 

Cret. and Tert. Fl.. p. 201, PI. XXXI. figs. 5-7. 
a Op. cit.. ]>. 287. 
sproc. I', s. Nat. Sins., Vol. V. p. 510. 



218 FOSSIL PLANTS OF THE ESMERALDA FORMATION. 

Cercis horealis has never been figured and the description is not full 
enough to make out its characters with certainty. 

As already stated, the form under consideration agrees most closely 
with C. pa/rvifolia and may be identical, but as its true shape can not 
be made out. I have ventured to give it a new name pending the dis- 
covery of new material. 

Locality: Northern base of the Silver Teak Range, I.:, km. north- 
east of Emigrant Teak. 

( IM'IKiMDUM '. TURNER] n. Sp. 
(PI. XXX, figs. 9-11.) 

Leaves of fine texture. Long-elliptical in outline, about equally 
rounded to both base and apex: strongly unequal sided al base; margin 
perfectly entire; petiole long, strong, and apparently slightly mar 
gined; nervation obscure, consisting of about two pairs of alternate, 
thin, irregular secondaries al an angle of about L-5 ; nervilles parallel, 
mainly percurrent. though often broken: liner nervation forming 
rather large quadrangular areas. 

This species Is represented in the collection by several examples, 
three of the hot being here figured. They appear to have been 
thickish leaves, rather long, elliptical in shape with abruptly rounded 
and strongly unequal-sided base. The length is :;.;> to 1 cm. and the 
width about 2 cm. The petiole is 8 to I", nun. longand apparently 
marginal. The nervation i- obscure, but i- well shown in the figures. 

This species ha- considerable resemblance to the genus Sapindus, 
but the petiole i- Longer and thicker than is usual in this genus, and 
it seem- to approach most closely to Cinckonidium. It appears to 
be allied t<> C. avalt Lx., 1 which, however, differs specifically in 
having a shorter petiole and a not so regularly elliptical form. But 
none of these specimens are very well preserved, especially as regards 
the finer nervation, ami they are referred tentatively to this genus. 

Locality: Northern base of Silver Peak Range, 3.8 and ■[.:> km. 
northeast of Emigrant IVak. 

Kill - '. \\ \ \DI.\slS II. Sp. 

PI. XXX, i 

Leaflet subcoriaceous, elliptical-obovate in shape, rather obtuse 
above, narrowed below to a narrowly wedge-shaped base; petiole very 
longand slender; margin with few remote low and rather obtuse teeth 
above the middle of the blade; midrib -lender, straight; nervation 
obscure, but apparently with several pairs of secondaries at an acute 

i n Land Tert. I ■■ 229, PI. XLVII. fig. 9. 



knowlton.] CONCLUSIONS. 210 

angle, and apparently terminating in the marginal teeth; remainder 
of nervation not discernible. 

The figured specimen is about 3 cm. in length exclusive of the petiole 
and 1.25 cm. wide, while the petiole is nearly 1 cm. in length. The 
outline is elliptical-obovate, narrowed below to a wedge-shaped base 
and an almost winged petiole. The margin is remotely few-toothed 
from above the middle. The nervation is very obscure, but apparently 
consists of small pairs of craspedodrome secondaries. 

I refer this form to the genus Rhus with some hesitation, as it seems 
unlikely that a leaflet would have a petiole of this length, but it agrees 
closely with Bhus fraterna Lx., 1 a species found at Florissant, Col- 
orado. In size, outline, and extraordinary length of petiole one speci- 
men agrees perfectly with this, but differs in having a few marginal 
teeth. The nervation is similar as far as can be made out. 

It is doubtful if Lesquereux's species belongs to JRhus, but it is so 
evidently similar to the one under consideration that I do not hesitate 
to put them in the same genus. 

Locality: Northern base of the Silver Peak Range, -±.5 km. northeast 
of Emigrant Peak. 

coisrciLirsioisrs. 

The fossil plants of the Esmeralda formation, as herein enumerated, 
embrace fourteen forms, all but one of which are regarded as new. 
This in itself is an unfortunate circumstance, since in determining 
their bearing on the question of the age of the beds dependence must 
be placed entirely on their recognized affinities and general facies. 
Hereafter it is hoped that the species here described may prove of 
value in fixing the age of other beds in which they may be found. 

The only species before recognized is Salix angusta Al. Br. , a form 
found in the European Miocene and since recognized in a large number 
of localities in this country, as the Green River group at Green River 
Station, Wyoming, and at various places in the Tertiary of Colorado, 
Wyoming, Montana, California, etc. On account of its wide distri- 
bution it is not of great value in fixing clearly the age of beds in which 
it may be found. 

The remaining forms described as new have been found to be refer- 
able in most cases to well-known living genera, which would argue 
for them a comparatively recent age. Thus we have Ohrysdbalanm 
pollardiana, which is regarded as quite close to the living C. icaoo L. ; 
( 'ercis nevadensis, perhaps closest to G. chinensis, though similar to 
occasional leaves of C. occidental™ of the Pacific coast; Qitereus turn, ri, 
which strongly suggests Q. turbinella Greene, a shrubby species of 
southern California and Arizona; also suggesting Q. duruosa ])ohj<-< vrpa 

1 Cret. and Tert. PI., 1884, p. 192, PI. XLI, figs. L,2. 



220 FOSSIL PLANTS OF THE ESMERALDA FORMATION. 

Greene and Q. undvlata Torrey of the Rocky Mountain region; 
Salix wccinifotia, undoubtedly allied to S. fiumatilis Xuttall (S. 
longifolia Muhlenberg), a species common throughout most of the 
region west of tin' Mississippi River; Sjpathyema ? nevadensis, which 
is supposed to be related closely to the eastern .V. feet Ida (L.) Raf. ; 
and Gleichi nia ? obscura, which is certainly similar to G. pohjpodioides 
Smith of the Cape of Good Hope. 

Of the others, the form described as Salix sp. is similar to Salix 
angwta and, Cinchonidhim f turneri is certainly allied generically to 
C. ovali Lesquereux of the Fort Onion group. 



PLATE XXX. 



PLATE XXX. 

Plants 'or the Ebmbralda Fobmation. p 

210 
.. 1-4. Gleichenia ? obecura n. sp 

5-7. Dryopteris ? gleichenoides D.sp 

- ,!i\ vaccinifolia D.sp 

«i-l i. Cinchonldium '.' tumeri a. sp 

!•_•. Quercus argentum n.sp 

L3. Salix sp 

II. Salix ?sp 

L5. Rhus '.' nevadensis o.sp 

1H. I'll known plant 

17. L8. Spathyema ? nevadensifl n.>i> „ 

L9. Chrysobalanuflpollardianan.sp - '' 

•id. Salix vaccinifolia n.ep 

21. Quercus turned n. >j> - 

■_'l'. Salix angusta ? 

areas? nevadensis n.^i> 

24,25. Unknown plant • 

26. Ficus lacustrie n. sp 

222 



U. 8. GEOLOGICAL SURVEY 



TWENTY-FIRST ANNUAL REPORT PART II PLATE XXX 




PLANTS FROM THE ESMERALDA FORMATION 



TMl MiLlOTYPf PRINTING CO., 1KXITON. 



DESCRIPTION OF A NEW SPECIES OF FOSSIL FISH 
FROM THE ESMERALDA FORMATION. 



Bv F. A. Lucas. 



The name L< uciscus turm ri is proposed for a small fish obtained by 
Mr. H. W. Turner, of the United States Geological Survey, from the 
Tertiary of the west side of the Big Smoky Valley in the Silver Peak 
quadrangle, Esmeralda County, Nevada. The type specimen, shown 
on PI. XXXI, B, is No. i302a, Catalogue of Fossil Vertebrates, United 
State's National Museum. 

In its general aspect the fish bears a strong resemblance to such 
small cyprinoids as Semotilus and Leuciscus, being of much the same 
general proportions as Leuciscus lineatus. The head, as in that spe- 
cies, is a trifle over 3£ in the total length; 1 depth of head, two-thirds 
of length. There are 19-20 precaudal vertebrae and 17-18 caudal, 
while Leuciscus lineatus and Semotilus atromaculatus have, respec- 
tively, 20-17 and 21-18. The tail is slightly forked; the lobes are 
slightly rounded. 

The anterior end of dorsal is in line with the anterior end of ven- 
trals, and the posterior end of dorsal is in line with the anterior end of 
anal. In Leuciscus the dorsal is directly over the ventrals and in 
Semotilus the dorsal is behind the ventrals. In both Leuciscus and 
Semotilus the anterior end of the anal is a little back of posterior 
edge of dorsal. The fin rays are as follows: Dorsal, 9; anal, 10; 
pectoral, 11-12; ventral, 9; caudal, 23. These may be compared with 
Leuciscus lineatus and Semotilus atromaculatus as follows: 



Leuciscus turneri 

Leuciscus lineatus 

Semotilus atromaculatus . 



1 According to Jordan and Kvermann the head is l; in the total length, but this does not accord 
with the specimen here vised lor comparison. 

223 



224 NEW FOSSIL FISH FROM ESMERALDA FORMATION. 

The greater number of resemblances are thus .seen to be to Li u- 
riscus Imeatus. 

It is quite probable that the wry fine rays of the pectorals have 
failed to make an impression, which would account for the lesser num- 
ber of rays in turneri as compared with others. 

Epineurals, epihsemals, and epicentrals are present, hut there arc no 
apparent traces of cpipleurals. nor should there be if the affinities of 
this fish are as they have been assumed. 

'The extreme length of the type specimen, which is of the average 
size, from tip of aose to center of caudal is 5^ inches; from tip of nose 
to process of last vertebra, 41 inches. 

With the exception of a few small fragments, it is the impressions 
of hones that are preserved and not the hone- themselves, and this fish 
is placed with the Cyprinidffi on account of its strong general resem- 
blance to that group of lishes. since the pharyngeal teeth have not in 
an\ case been found. For the same reason it is kept in the genus 
Leudscus, as no sufficiently good characters can he assigned to these 
specimen- to warrant the establishment of a new genus. 



PLATE XXXI. 



21 GEOL, PT '2 15 



PLATE XXXI. 

SPECIMENS OP LkICISTIM n-RNERl LlTCAH, FROM I'll K EBMEBAL'dA FORMATION. 

All natural size. 

\. Specimen showing detailw of pectoral fin. 

B. Type Bpecimen. 

( '. Specimen show ing details of vertebra; and ribs. 



U. S. GEOLOGICAL SURVEY 



TWENTY-FIRST ANNUAL REPORT PART II PLATE XXXI 



' 









FOSSIL FISH FROM THE ESMERALDA FORMATION 
LEUCISCUS TURNERh 



TMl HELIOTYPE PRINTIHO CO.. BOSTON. 



MIWERAL VEIN FORMATION AT BOULDER HOT SPRINGS, 
MONTANA 



WALTER HARVEY WEED 



CONTENTS 



Page. 

Introduction 233 

Quartz and jasper veins of Boulder region 234 

Distribution 234 

( renesis of the reefs 234 

Existing hot springs 234 

B< udder I [< it Springs 235 

L< xatii in and general features 235 

< >ccurrence of springs 236 

( lharacter of water 237 

Hot-spring fissures 238 

Fissure tilling 239 

Nature of the vein tilling 240 

Rock decomposition effected by hot waters 244 

Relation of altered granite to vein fissures 245 

I reneral character of the altered rock 245 

Metasi miatic alteration of the granite and aplite 246 

Origin of the vein-forming material 24s 

( mid and silver contents of the veins 24S 

Recent movement or faulting of the veins 249 

Theory of ore deposition iii mineral veins. 249 

Microscopic petrography of the altered rocks and vein tilling 252 

The altered granite 252 

Sericite 253 

Kaolinite 253 

Fibrous silica 253 

The jasperoid 253 

The filling 254 

Structure of filling 254 

229 



ILLUSTRATIONS. 



Page. 
Plate XXXII. Boulder Hot Springs, Montana 234 

XXXIII. Topographic map of Boulder Hot Springs 238 

XXXIV. A, Specimen showing brecciation of hot-spring deposit by 

later movement along vein; B, Cellular deposit of silica 
formed in calcite deposit from which lime carbonate has been 
extracted by acid, leaving skeleton of silica plates funned 
along calcite cleavages; < \ Specimen showing weathered 
surface of hot-spring deposit cm which the calcite has been 
dissolved away by weathering and the silica plates left in 

relief 240 

FlG. 6. Index map of Montana, showing location of the Boulder Springs 235 

7. Ideal transverse section of hillside, showing occurrence of hot-spring 

vein 236 

8. Xetted fracturing of granite alongside of vein exposed in shaft on hill- 

side, Boulder Hot Springs 238 

9. Cross section showing concentric layers of deposit found about upper 

Springs in middle gulch, Boulder Hot Springs 240 

10. ('rusts formed by hot waters about granite nuclei 241 

11. Specimen showing fragments of granite incrusted by a hot-spring 

deposit 241 

12. Specimen showing occurrence of crusts formed by a hot-spring deposit, 

and of the alteration of calcite. with the formation of secondary 
cpiartz upon the plates 242 

13. The red "jasper" deposit shattered by later movements along the vein 

and the fragments cemented by newly formed opaline silica and 

quartz 249 

231 



MINERAL VEIN FORMATION AT BOULDER HOT 
SPRINGS, MONTANA. 



By Walter Harvey Weed. 



INTRODUCTION. 

The origin of metalliferous veins by hot waters ascending from 
great depths has always been a favorite theory with the practical 
miner, however widely the pendulum of geologic theory may swing 
a way from this side of the arc of thought. Nevertheless, although 
hot springs are of as world-wide occurrence as ore deposits, examples 
of ore deposition by hot springs are rare. Indeed, the only examples 
generally recognized are the familiar ones at Steamboat Springs, 
Nevada, and Sulphur Bank, California, though the fact that hot waters 
can dissolve the metals and form ores is established by the observa- 
tions of Paubrec. Tn a study of the hot springs of the Yellowstone 
National Park, begun in 1883 and continued for over seven years, the 
writer sought diligently for some evidence of ore deposition. It was 
found that veins of pyrite were forming in fractures in the rhyolite at 
the Norris Geyser Basin, and that subsurface deposits of realgar and 
orpiment, and surface deposits of scorodite, as well as calcareous and 
siliceous sinters, were forming at several localities, but no ore deposits 
were found forming, nor were any quartz veins found, nor was any evi- 
dence discovered to show the genetic connection between hot springs 
and veins. The writer was therefore much gratified in 1897 to find a 
hot -spring locality where the waters are still actively at work forming 
veins, analogous in every way to those which are commonly found in 
the adjacent mineral districts and which often constitute workable ore 
deposits. The deposits now forming do not, it is true, carry large 
amounts of the precious metals, but gold, silver, and copper do occur 
in appreciable amounts, and it is evident that we have a new locality 
where mineral deposits — although not of economic value — are now 
being formed. The locality is also interesting as the only known 
example in this country of the deposition of zeolites by hot spring 
waters. A no less important process now in operation is the metaso- 



234 MINERAL VEIN FORMATION AT BOULDER HOT SPRINGS. 

matic replacement of granite by the hot waters, forming the zone of 
replaced rock which is so common a feature of the quartz veins of the 
region and in which the workable ores of the veins of the region 
commonly occur. 



QUARTZ AM) JASPER A'EINS OF BOULDER REGION. 

Distribution. -Throughout the granite district of Jefferson County, 
Montana, a region which extends from Helena on the north beyond 
Butte on the south and is L5 to 20 miles wide, there are scattered areas 
where the granite is more or less disintegrated and weathered down to 
smooth slopes. I hese areas frequently show reefs or dike-like masses 
of quartz and jasper which project above the surface and are often 
traceable for a mile or more. The larger reefs frequently form the 
crests of ridges and determine the topographic relief of the neighbor- 
hood. Often they show a general parallelism, though in other instances 
they form a network corresponding to three distinct fracture, systems. 
In the Lump Gulch silver district, a few miles south of Helena, the 
rich silver-lead and ruby-silver ores are found in such veins, and at 
various other localities in the region the great productive ore deposits 
occur in them. as. for example, the Comet mine. Gray Eagle, Bonanza 
Chief, Liverpool, etc. When carefully examined these reef s show a 
central core or vein of crystalline quartz which varies from a few 
inches to several feet across. On both sides of tins the reef material 
is generally in part a jasperoid. while the greater part shows a marked 
granitic texture and is clearly an altered granite in which feldspar and 
some of the original quartz of the rock has been altered to a white. 
clayej substance. The rock, though highly silicified, shows that it is 
a i lift a somatically altered form of the neighboring gran it e. Very com- 
monly the reef rock is shattered and possesses a marked brecciated 
structure. 

Genesis <>/'//>> reefs. The origin of these reefs or veins was for a 
while a puzzle to the writer. Thej possess none of the characters of 
hot-spring deposits observed in the Yellowstone: no sinter deposits 
were found in connection with them, nor do they show any concentric 
banding or the structural characteristics which characterize the usual 
material tilling hot-spring conduits. In brief, the veins show none of 
the features commonly characteristic of hot-spring action or deposits. 

Keisting hot springs. Existing hot springs are found at a number 
of places near the borders of the granite mass, notably at Pipestone, 
Helena, and Alhambra. and at the Boulder Hot Springs. Near Butte 
hot waters issue from the granite and are probably connected with 
later rhyolite intrusions. At all these localities except Boulder an 
examination of the springs threw no light upon the question of the, 
origin of the quartz veins. At Boulder, however, veins are found 







f J ; i 


i 


ml] 


; 


J. M 


^ 


Mi & 









LOCATION OF THE SPRINGS. 



235 



whose connection with the hot springs is undoubted. The hot waters 
still till fissures marked by such reefs, and are now forming deposits 
whose weathered outcrops present all the features of the ore-bearing 
veins, while assays of the vein filling and of the altered silicitied granite 
alongside of the fissure show the presence of gold and silver in appre- 
ciable though small amounts. 



BOULDER HOT SPRINGS. 

Location and general features. — These hot springs are situated in 
Jefferson County, Montana, about midway between the cities of Butte 
and Helena, on the southern side of the Boulder Valley and near the 
Boulder River. The springs are 3 miles from Boulder, a town on 




. 6. — Index map of Montana, showing location 



|iriiiK> 



the line of the Great Northern Railway and on a branch line of the 
Northern Pacific Railway. The place has been improved by a com- 
fortable hotel and bath houses, and it is a summer resort as well as a 
place for the treatment of invalids. The slopes of Bull Mountain rise 
abruptly to the south, and on the north the broad, green meadows 
of Boulder Valley form a pleasing foreground for a mountain pano- 
rama of great beauty (PI. XXXII). 

The hot waters issue from granite at a point a few miles distant from 
its contact with the older andesitic rocks of Bull Mountain. The rock 
is a typical coarse-grained granite, consisting of orthoclase feldspar 
and quartz with lesser amounts of plagioclase feldspar (andesine), 
brown biotite-mica, and green hornblende. Magnetite, titanite, and 
apatite arc present as accessories. 



236 MINERAL VEIN FORMATION AT BOULDER HOT SPRINGS. 



This granite is sheeted by well-defined joint planes, which, in the 
vicinity of the spring, have a course of N. 85° E. These joints cause 
the formation of very rugged slopes, with picturesque groups of mon- 
oliths and bowlders at various localities near by, and to a less extent 
close about the springs, hut in the hot-spring area itself the granite is 
weathered down and does not form conspicuous outcrops. 

The hot-spring area does not show any of the sinter deposits common 
about other hot-spring areas. The larger springs near the hotel have 
no deposits at all. The group a quarter of a mile from the hotel and 
that 200 feel about it on the mountain slope are marked by low lines of 
grayish material a few feet wide, showing in some places as a reef or 
wall a few feet high: and rust-stained jasperoid reef s also occur. The 
area between these reefs and the hotel is strewn with fragments of sili- 
ceous and calcareous material from the upper fissures and from old 
hot-spring fissures which also traverse this ground. The distribution 
and course of only the larger veins are shown on the map (PL 

XXXIII: 



■« i 



mm 






mm 



Occurrence of springs. The hot springs at Boulder occur in two 
groups. ( )ne <>!' these groups is close to the hotel, the waters flowing 
from granitic debris a few feel in thickness resting on solid granite. 
The waters issue from a slight depression or gully a few feet below 
the general level of the slope. The largest spring has a temperature 
of 164°, and is the one supplying the bath houses. A measurement 
of the amount of water flowing from this spring was not possible 
because it supplies the bath houses and hotel through a system of 
pipes. A large amount of water flows away and is not utilized. The 
second group of spring- lies at an elevation of about 200 feet above 
the hotel, the vents being in two small gulches which indent the 
slope, as shown on the topographic map (PI. XXXIII). This upper 

group is much more interesting, though the c position of the water, 

so far as known, is quite the same a- that of the spring near the hotel. 
Thesesprings are situated on lines which clearly indicate their connec- 
tion with fissures crossing the granite. 



weed.] CHARACTER OF THE WATER. 237 

Iii two cases the hot waters issue from the western end of fissures 
marked for several hundred feet along the surface by deposits of 
silica and of calcite. Other springs issue from the southern border of 
a fissure whose outcrop is also marked by a low and inconspicuous 
deposit of sinter. The most easterly group is near the log cabin 
shown on the map (PI. XXXIII). Here the springs flowing were 
naturally rather small, and an attempt was made to develop water by 
artificial means. For this purpose two shafts were sunk to a depth of 
10 to 20 feet on the edge of one of the hot-spring reefs and a tunnel 
was driven into the hillside to tap one of the reefs. Another artificial 
opening was made on the western end of one of the upper reefs, where 
it came to the head of one of the gulches, and a pit 5 or 6 feet deep was 
sunk into the slope. In each instance hot water was obtained, although 
none whatever showed on the surface, and the fissures were to all 
appearances dry and the springs dead. 

At none of the springs is there any surface deposit of moment now 
forming. It is true that at one or two of the most active vents a very 
slight crust is being deposited in connection with the vegetable matter 
present. If the hot waters are forming an} T considerable deposit, 
as would be indicated by the composition of the material found in 
the tunnel, deposition must be taking place within the fissures them- 
selves and not on the surface. The hot-water streams all contain 
alga? of the usual brown, green, and orange tints in the channels run- 
ning from the vents. These algye possess the same characteristics as 
those found in the Yellowstone hot springs, but no specific determina- 
tion has been made of them. Singularly enough, they are not build- 
ing up any of the great jelly-like deposits of silica found in the Yel- 
lowstone, although it is known that the waters contain considerable 
silica in solution. The brilliant colorings of these algae, like those of 
the Yellowstone Park, show a definite relation to the temperature of 
the water. The red and brown colors are, as usual, ascribed by the 
ordinary visitor to the presence of iron in the water, but samples of 
the material when dry lose their color and upon heating are shown to 
be merely organic material practically free from iron. 

Character of water. — The hot spring waters are clear, colorless, and 
tasteless. The temperature varies from 161° at the big spring near 
the hotel to 120° in one vent in the hillside group. The outflow from 
one of the reefs is 152° and that from another 158°. In outflow from 
the tunnel the water has a temperature of 110°. The waters have a faint 
odor of H 2 S at the spring, but it is not noticeable elsewhere, although 
the blackening of paint, etc., shows that this is present. The waters 
do not, so far as could be determined, form any surface deposit of 
sinter. The conduit pipes used to carry water to the hotel are entirely 
five from sediment, and in fact are corroded by the waters to a slio-ht 
extent, as is shown by an iron staining of the porcelain tubs and basins. 



238 MINERAL VEIN FORMATION AT BOULDER HOT SPRINGS. 



The analysis published by the hotel proprietor is as follows, the con- 
stituents being stated in grains per wine gallon. The name of the 
analyst is not given. 

Chloride of sodium 4. 7 

Sulphate of soda 4. 3 

Carbonate of soda 2. 6 

Carbonate of lime 1-3 

Carbonate of magnesia 3.6 

4. 8 

_ 2. 9 



Sulphur 
Iron 




Hot-spring fissures. The larger spring, the one nearesl the hotel, 
does not appear to be on a recognizable fissure; the other springs, 
one-fourth of a mile distant, flow from fissures which maybe recog- 
nized by the deposit, although the fracture is not open at the surface. 
These fissures are clearly traceable across the slopes by their definite 
lines of deposit. Their course varies from nearly east-west in 
the three parallel and uppermost reef- to northwest in the fissures 
ending near the little reservoir. The 
latter course accords Dearly with the 
pronounced sheeting seen in the gran- 
ite near by. The courses of the different 
fissures when compared are found to 
make angle, of 23 . 48 . 60 . 85 . and 
L08 with one another. Compared with 

the lissures of the granite where no hy- 

drothermal action has taken place in the 

immediate vicinity of the springs, there 
i- not entire concordance, the granite 
showing courses of sheeting of N. 30 . 
45°, 49 W., the first two readings being taken near the bath house 
and the last one near the easternmost fissures. It is at once apparent 
that, like the jasper reef, observed through the adjacent districts, the 
course of these hot-spring fissures i- not uniform, and that, while 
certain courses conform to the dominant sheeting of the granite, 
others correspond to intersecting fracture planes not common in the 
general granite area. In areas of well-jointed granite the most pro- 
nounced sheeting fractures of the granite have vertical walls, while 
the lesser joints are inclined toward one another at 45 . Where it 
was possible to make observations upon the outcrops of these hot- 
spring veins (and in one instance a 20-foot shaft exposed a good sec- 
tion of the vein), it was found that the reefs running N. To E. have 
vertical wall-, while those whose course is N. 38 W. dip To to the 
south, and a fissure whoso course i- N. 22 E. has a dip of To to the 
west. It i- therefore evident that they do not conform in dip to com- 
pression joints of the granite. 



Fig. 8.— Netted fracturingof granite along- 
side of vein exposed In shaft on hillside, 
Boulder Hoi Borings. 



U. S GEOLOGICAL SURVEY 



TWENTY-FIRST ANNUAL REPORT P A R T II P L . XXXI 




MAP OF BOULDER HOT SPRINGS AREA 

BOULDER, JEFFERSON COUNTY; MONTANA 



Contour interval 5 ft. 
Surveyed Aut>. L898 by W.J.Lloyd 



THE FILLING OF THE FIS8UEES. 239 

Shafts and a short adit or tunnel, run into the hillside, show that 
the rock adjacent to the vein fissure is sheeted by rudely parallel and 
cross linked fractures. The accompanying diagram, fig. 8, shows 
the fractures seen in the west wall of one of the shafts. In the wall 
of the, deepest shaft the fractures are 8 to 10 inches apart, but appear 
to be closer together near the bottom, and all run parallel to the vein 
walls. So far as observed these link fractures are not the result of 
intersecting diagonals 45 apart, such as are so common in the rocks. 
They may result from an irregular fracturing of the rock due to shearing 
movement. 

The plan of the vein or fissure outcrops, like those of the jasper 
reefs observed at a number of localities about the Boulder Valley, shows 
an irregular checking of the country rock and seems to indicate tor- 
sional strain and not simple shearing. The length of the hot-spring 
fissures, as indicated by the deposits, is not very great. In no case 
was such a fissure traceable over a few hundred feet, although a reef 
has, in one or two instances, been observed on a direct continuation 
of the line of a fissure beyond its apparent termination. 

'Fissure filling. — The fissures are known to be, hot-spring conduits, 
because hot water is now flowing from several of them. Most of the 
fissures are, however, sealed up by the hot- water deposit formed when 
they were filled to the level of the present surface. This fissure filling 
forms a vein; it is only by means of this deposit that the fissures may 
now be traced. The material varies somewhat in outward appearance, 
as it does in mineral composition. As seen in outcrop it is for the 
most part of a light-gray color and appears in contrast with both the 
green marsh of the hollows and the gravelly granitic debris which 
covers the dry slopes. The deposit does not weather in conspicuous 
relief, except at the extreme southeast corner of the area mapped, 
near a log cabin. At this locality there are several reefs or walls. 
None of them are as large or as persistent as some which may be 
found in adjacent mineral areas, though quite conspicuous, so that 
even when the wall is broken down the course of the fissure may be 
followed by a continuous line of deposit. Above the log cabin there 
are three parallel fissures, marked by white outcrops and having a 
course of very nearly N. 70° E. The lower of these three veins is 
from 5 to 7 feet wide, and in some places is weathered in relief as a wall 
3 to 4 feet high. The vein can be traced westward down the slope 
until lost in a pit cut into the slope, an opening which taps the hot 
water of the vein and affords a supply utilized by the present owners 
of the property. At this point the deposit is 2£ feet wide and has a 
fibrous or thatch like structure and is shot through with needle-like 
masses of silica which give it a peculiar felty appearance. The sec- 
ond fissure, which is 24 feet distant and farther up the hill, is but from 
10 to 19 inches wide at its east end and stands up a few inches above 



240 MINERAL VEIN FORMATION AT BOULDER HOT SPRINGS. 

the surface. Farther west the vein outcrops as a mass 15 to 24 inches 
wide and forms a wall about 5 feet long and 2£ feet high. It shows' a 
well-defined vertical north wall, and traverses aplite in part and granite 
beyond. Still farther west the vein forms a low wall 3 to 6 feet wide, 
where the light-gray color of the deposit is in strong contrast to the 
grassy slope. The concretionary structure is very marked in some 
cases and shows successive crusts formed one upon another, as is seen 
in the west end of the fissure in the middle gulch (tig. 9). 

Overmuch of the area scattered fragments of jasper, chalcedony, and 
other material that is readily recognized as hot-spring deposit indicate 
other reefs which have not been located. Moreover, there are several 
old reefs on the terrace above the Little Bowlder River east of the 
limit of the map, and several veins of hot-spring deposit were recog- 
nized on a ridge which runs up from the center of the hot- spring area. 
As, however, the prominent reefs mentioned and those connected with 
the existing outflows of hot water show all the characteristics of the 
others, and there is no doubl as to their origin, no further mention of 
the extinct hot-spring fissures will be made. The width of the fis- 
sures, as indicated by well-recognizable hot- 
spring deposit, thi' true \ein tilling, is varia- 
ble. As slated above, it is from a few inches 
to several feet in one of the reefs, and in other 
cases a width of 1l' feet has been measured. 
In general, however, the clearly recognizable 
deposit does not exceed 2 or ."> feet. 

Xatim ofth-rein U'lUm/. As noticed in the 
centric layers of deposit (omul ." .' 

aboot upper springs in middle Introduction, tile deposit found about these 
Bnlch. Boulder Hot Springs. ) )()t 8 p rm g Sj the origin of which is unques- 
tionably due to the springs themselves, Is not of the ordinary type. 
In some places the reefs do, it is t rue. -how a deposit of calcite having 
thatch-like structure, like that of the travertines of the Mammoth Hot 
Spring, hut in general the deposit is hard, and consists of a white or 
dark-gray substance intermixed with more or less red jaspery material 
iii bands and patches, sometimes carrying included fragments of 
slightly altered granite, hut in large part consisting of a white crys- 
talline substance which is found to he a mixture of chalcedony and 
stilbite. [n external appearance the deposit varies greatly. At the 
lower of the three veins above the log cabin, already mentioned, the 
deposit IS gnarled and knotty, has a concretionary structure about 
central points, as illustrated in figs. LOand Li, and. is very dense, though 
showing a crystalline structure on fresh fractures. In part it appears 
to be chalcedony and in part it is quartz, hut a large portion of this 
deposit consists of a gray calcite which, when fresh fractured, shows 
thin films of silica traversing it in a network, hut which on weathered 
surfaces shows a honevcombed or cellular structure much like that 




U. 8. GEOLOGICAL SURVEY 



TWENTY-FIRST ANNUAL REPORT PART II PLATE XXXIV 




DEPOSITS FROM VEIN FISSURES, BOULDER HOT SPRINGS, MONTANA 



THE HEUOTYPC PH.NT'NO CO.. BCX1TUV 



NATURE OF THE VEIN FILLING. 



241 



of the quartz of certain mineral veins (PL XXXIV), notably of the 
De Lamar of Idaho, the Elkhorn of Montana, and the Drum Lummon 
of Marysville. The weathered deposit also shows at times a mossy 




Fig. in.— crusts formed by hot waters about granite nuclei, a, Stilbite and silica; 6, curly textured 
opaline silica; c, opaline silica; d, calcite. 

surface, with distinct crusts and bands of silica, and also fragments of 
a chert-like substance projecting in relief above the general surface 
of the rock. Opaline; silica also appears irregularly distributed in 





6 INCHES 



Via. 11. — Specimen showing fragments of granite encrusted by a hot-spring deposit. The deposit 
consists of layers of silica and .if stilbite mixed with silica. The la vers are well marked, and some.'. 
them are tinted by small amounts of iron oxide, so that a distinct concretionary .structure is appar- 
ent. '1 be crOSS-hatChed areas are calcite. Drawn from nature; one-half natural size. 

bunches through the mass, as well as in bands and curly layers. On 
fresh fracture it is usually dark gray and very hard. The upper reef 
shows included fragments of granite, the fragments ranging from 
21 GEOL, l'T 2 16 



242 MINERAL VEIN FORMATION AT BOULDER HOT SPRINGS. 



several inches across up to one which was 10 inches wide and 3 feet 
long. In these fragments the granite is but slightly altered, showing 
the hornblende changed to chlorite or a green earthy substance. The 
biotite is clearly recognizable, though partly altered and bronzy in 
color, while the feldspar shows alteration along cracks and seams. The 
specimen illustrated in fig. 11 was taken from this vein, and shows 
quite clearly the normal breccia structure of a mineral vein. 

One of the reefs lying to the southeast of the log cabin and parallel 
to the gully which runs down the slope at this place is a typical silica 



or jasperoid reef. It 
fragments of granite 



consists of a 
cemented by 







breccia, or more or less altered 
a dark-brown jasper, which in 
the weathered outcrop appears 
to he largely brown and red 
iron oxide. The reef wall dips 
at 65 to To . A cross section 
shows a hand a foot wide of solid 
jasper with irregular colored 
banding, shading on the east side 
into a brecciated material. This 
breccia clearly shows the re- 
placement of granite fragments, 
hut there is undoubtedly also a 

Pi6.12.-Spoctau5n showing cruste formed bya hoi shattering of the original de- 
gpring deposit, and the alteration of calclte, with posit. This reef can he traced 
tlu- formation of secondary quarts upon tin- ,. . . »» » . , i . 

plBtes for about to tee! up the slope 

from the shaft in its lower end. 
At one place, where it has been opened by blasting, it shows a seam 
90 to its course, and here is seen to consist of altered granite like 
that which will be mentioned later in discussing the alteration of the 
granite adjacent to the veins. The cross fractures here are filled with 

secondary silica. The ledge appears to wedge out southward and not 
to run into splits and stringers, though lilms of chalcedonic silica 
were observed running oil from the end into the apparently unaltered 
granite. 

The jasper like deposit is brick red to dark red in color, but when 
examined under the microscope is found to consist of a very tine paste 
of altered rock fragments, together with more or less cryptocrystal- 
line silica. The siliceous bands seen are in part true chalcedony and 
in part opaline amorphous silica. Quartz veinlets also occur in the 
i-ed jaspery material, and abundant quartz of the typical vein-quartz 
type was seen scattered over the surface, though none was actually 
found in the hot-spring deposit itself. 

A large part of the hot-spring deposit consists of calcite which is 
netted with sili<a films. As already noted, the structure of this mate- 
rial is peculiar. The weathered surface is shown on PI. XXX1Y. ('. 



weed.] ANALYSES OF THE VEIN FILLING. 243 

and in detail in the diagram, tig. {2. When the fresh material is 
treated with dilute hydrochloric acid the calcite is entirely removed, 
leaving a cellular material consisting of almost pure silica, the struc- 
ture corresponding very nearly to that of the weathered outcrop 
and to that of the vein quartz noted at various localities, as shown in 
PI. XXXIV, B. In this material, of course, the films of silica are 
extremely thin, rarely exceeding the thickness of a sheet of paper, 
and are very fragile. There is none of the crystalline coating- or 
drusy surface observed in the weathered material, or in the De Lamar 
quartz. An analysis of the substance gave — 

Per cent. 

( !a< !0 9 - 81. 16 

Mn0 2 - 34 

Insoluble in HC1 18. 50 

100. 00 
An analysis of the insoluble material yielded — 

Per cent. 

Si0 2 87. 7 

A1 2 3 8.4 

Cad 3. 9 

100.0 

The zeolite material is mostly pure white or cream-white, but is 
sometimes stained pink or red by ferric oxide. It has a distinctly 
crystalline or granular structure and in hand specimens often resembles 
the aplites of the region. It seems to form the greater part of much 
of the deposit, but is intimately mixed with silica. A determination 
of this material, made in the chemical laboratory of the Survey, shows 
the following composition: 

Per cent. 

Silica 87. 2 

A1 2 3 4. 

CaO 1.5 

K 2 0. 3 

Na 2 0. 7 

Insol. not Si0 2 1.2 

Loss on ignition 4.9 

99.8 
Silica soluble in Xa 2 C0 3 after treatment with HOI 6.3 per cent. 

Disregarding the admixture of silica, the analysis shows the silica, 
alumina, lime, soda, and moisture to be present in the following 
proportions: 

Per cent. 

Si0 2 6. 3 

A1 2 3 4. 

CaO 1.5 

Xa,< > 0. 7 

11,0 4. 9 



244 MINEKAL VEIN FORMATION AT BOULDER HOT SPRINGS. 

The zeolite is therefore stilibite. and the deposit consists of this 
mineral mixed with chalcedonic silica. 

About the veins where the hot water is now flowing little if any 
deposit is actually forming, though the waters issuing from the fissure 
ending at the reservoir seem to be adding to the fissure deposit at that 
place. The nature of the material carried in solution by the waters 
can, however, be judged by the deposit now forming in the walls of the 
tunnel driven into the hillside near the log cabin. This deposit forms 
as an efflorescence without crystalline structure, having a moss-like or 
mammillarv appearance, coating the warm and altered granite walls. 
It is almost pure white, tin. ugh stained in some places by fragments 
of altered granite and more rarely by brilliant red iron oxide. An 
analysis was made in the Survey laboratory, with the following results: 

Per cent. 

Soluble in water ss. l'7 

Soluble in hydrochloric acid I equals * 'a( '< >., ) .">. 72 

Insoluble in 1 It 1 (equals SiO„ etc.) 1 6.01 

100. 00 

The composition of the material soluble in water is as follows: 

Per cent. 

t7.LV. 

N CO, 28.33 

V" I 1.09 

CO, L.96 

25 

Difference, mainly II < > 9, :;',i 

SS. L'7 

The <'( >, i- in excess of thai making norma] carbonate. 

This deposil clearly shows that the waters are leaching out soda 
from the granite, and accords with the microscopic examination of 
these rocks as described later. The substance whose analysis has just 
been given \\a> tasted in the held, a- it w as' suspected that it was a 
carbonate or sulphide, bul it was apparently tasteless. It is believed 
that this is because the silica occurs as thin films or concentric shells 
formed by evaporation upon the surface of the deposit. 

/,'<»■/,- decomposition effected by /><>/ waters. -The granite adjacent 
to the hot-spring fissures is much altered by the hot waters. This 
is well shown by the exposures formed in the three shafts sunk 
alongside the veins and li\ the open cut made in one end of a vein. 
and also by the pits sunk in the altered granite at the head of the 
western hot-spring gully. In general, however, this hot-spring 
locality is lacking in those areas of broad and profound fumarolic 
or solfataric alteration where steam or acid vapors are ascending, 
usually found in such districts, and so common throughout the Yellow- 

".«> percenl silica. 



weed.] CHARACTER OF THE ALTERED ROCK. 245 

stone Park. It should be stated, however, that the surface wash of 
the disintegrated granite partly covers the slope and hides all evidence 
of rock alteration. 

Relation of altered graniU to vei/n, fissures. The exposures seen in 
shafts, tunnel, and open cut show that rock alteration has taken place 
along the fractures winch net the rock. The conditions seen in the 
tunnel and in the shaft 200 feet or so from the cabin show that the 
granite is more or less generally permeable, as if it were disintegrated 
to a coherent but loose-textured mass. In most cases the reddening 
of the rock is confined to the seams which traverse it and occurs in 
bands one-quarter inch to 2 inches in width, the transition to the less 
altered nucleal bowlder being gradual. These red seams commonly 
hold a central film of iron oxide or silica, and sometimes a jasper-like 
substance. In the tunnel the rock is more generally altered. It shows 
parallel and linked fractures marked by films of silica .01 mm. wide. 
The different rhombs between fractures vary one from another in 
color, and are sometimes mottled. The tints are reds, orange, yellow, 
and the various tones due to iron oxides. The rock is coherent, but 
crumbly under pressure, and quite thoroughly disintegrated through- 
out the entire length of the tunnel. It is saturated with warm water, 
which is of course most abundant near the face of the adit. 

In some instances the granite, though altered, is still gray, and the 
fractures are defined by flows of pale-yellow chalcedonic silica. 

General character <>ff/tr altered rod-. — The altered granite is abun- 
dant in the dump heaps of the shafts. It is commonly of a red-purple 
or sometimes a yellow tint, or is mottled with these colors. Its most 
marked feature is a stippling of the rock with white spots, which often 
show a rectangular outline. These spots give the rock a decided 
porphyritic appearance. They are creamy white on surfaces exposed 
to the weather, but on fresh fracture are seen to be due to pale-greenish 
irregular masses with the greasy luster of sericite. Aplite, too, is 
much altered, having usually a very pale greenish or pink color and 
showing to the eye abundant sericite. These altered rocks, if com- 
pared with the fresh granite of the region, show a similar structure, 
but there is a marked absence of hornblende, augite, and biotite. The 
feldspars are replaced by the pale greenish-yellow sericite masses and 
the quartz is shattered and in part eaten into and replaced by sericite. 
All gradations to fresh granite may be seen, in which the mode of 
attack of the feldspar and quartz is apparent. About fractures there 
is a local concentration of the iron. In the most brilliantly colored 
specimens of the altered granite the rock shows only white kaolin, 
some glassy quartz, and a red groundmass. The kaolin corresponds 
to the sericite. and the red band is largely shattered quartz with the 
fractures tilled by iron oxide. 



246 MINERAL VEIN FORMATION AT BOULDER HOT SPRINGS. 

Examinations of thin sections of the rocks in various stages of 
alteration show that metasomatic replacement is actively going on. 
That it is due to the hot spring waters seeping- into the shattered wall 
rock of the veins there can be no doubt. The evidence of the slides 
shows that the granite is being sericitized. Not only are the horn- 
blende, biotite, plagioclase, and orthoclase attacked in the general 
order given, but the quartz is abundantly attacked and is being altered 
to sericite- a phenomenon discussed by Lindgren for the altered 
rocks of ore deposits, but never, so far as known to the writer, 
described as a result of actual hot-spring action. The hoi spring 
waters are actually altering the granite and removing its soluble con- 
stituents. In the lack of a good analysis of the water we can judge 
its contents by the deposit now forming on the walls of the tunnel. 
This consists chiefly of sodium sulphate, together with sodium carbon- 
ate (in part bicarbonate). :i very little sodium chloride, and calcic car- 
bonate and silica. The waters are therefore plainly alkaline, and, as 
shown by comparison of the fresh and decomposed granite, are leach- 
ing the rock, carrying part of its substance oil and concentrating the 
insoluble material in the open spaces. While, therefore, the deposits 
are in large part the tilling of open fissures and show crustification 
and handing, and at times contain coated fragments of country rock, 
there is also extensive metasomatic replacement, or the formation of 
deposits due to such action. 

Slides of both the vein tilling and the altered granite have been sub- 
mitted to Mr. Lindgren for examination, as he has probably studied 
the decomposed rocks about mineral deposits more than any other 
geologist in this country. He finds that the vein filling consists partly 
of quartz of medium coarse grain, with which are intergrown prisms 
and imperfect crystals of stilbite. The double refraction of the latter 
mineral is weak. A.dular feldspar also occurs in a little veinlet. 

.}/, tasomatic alU ration of the granitt andapUte. — The granite adjoin- 
ing the vein is considerably altered, the alteration consisting in the 
development of two minerals, sericite and kaolinite. Either of the 
two may locally predominate, and both the feldspar and the quartz 
are being attacked and replaced by these minerals. There are no 
remaining ferromagnesian minerals, their place being taken by kao- 
linite and sericite. Tufts and needles of rutile are mixed with this 
mass. The alteration usually begins between the grains and gradually 
eats into them. Long tufts of radial sericite may develop in the 
interior of orthoclase crystals. A grain of pyrite and some copper 
stain were noted in the altered granite. There is practically no cal- 
cite in the altered rock, and it seems that the calcic carbonates result- 
ing from the soda-lime feldspars must have been carried out into the 
fissure and there deposited. 



weed.] METASOMATIC ALTERATION OF ROCKS. 247 

To the eye the sericite is apparent on exposed musses as white clayey- 
looking spots, which give the rock ;i porphyritic appearance. On 
freshly fractured surfaces these spots are of a pale-green tint. Under 
the microscope thin sections show that all the minerals of the granite, 
including quartz, are attacked. The dark-colored minerals have 
entirely disappeared, the smaller anhedra of orthoclase and the plagio- 
clase are nearly gone, and the large orthoclase masses and quartz are 
eaten into and show tufts and masses of sericite in cleavage cracks and 
in apparently isolated patches in the center. 

Sericite. as the minutely fibrous or tufted variety of muscovite is 
called, is the most common of all the minerals resulting from the altera- 
tion of rocks by vein waters. Critical examination of the so-called 
clays and talc and of much of the "kaolin" of most mineral veins 
shows that they consist largely of sericite, which is nearly insoluble and 
forms from all the common rock-making minerals, though it is most 
readily formed from feldspar. It may be formed by waters holding 
C0 2 simply, but more commonly alkaline carbonates as well. In the 
first stages of attack it is seen as a clouding of the mineral, and as tufts 
and scales along cleavage planes, or as strains in cracks, but finally it 
invades the whole ciystal and reduces it to a felted mass of sericite 
fibres. For orthoclase, Rosenbusch gives 1 the following equations as 
representing the change: 

K,A] 3 (Si 3 8 ) 3 +H 2 0+C0 2 =KH 2 Al 3 (SiOJ 8 +K 2 C0 3 +6Si0 2 . 

Sericite is readily formed also from plagioclase, the potassic carbon- 
ate formed by the foregoing reaction replacing lime, and the latter 
substance forming calcite in situ or being carried off by the hot spring 
waters as bicarbonate, to be deposited, as it is at Boulder, as vein 
filling. This reaction is as follows: 

Anorthite-f-OrthoelaHe-fCarbon dioxide -f- Water =Calcite+Sericite+Quartz. 
Ca ALSi, 8 +K Al Si 3 8 +C0 2 -|-H 2 0=Ca C0 3 +H 2 KAl 3 Si 3 12 +2Si0 2 . 

The hornblende and augite of the granite probably alter first to 
chlorite and this to sericite and pyrite, or in the presence of oxvgen 
to limonite. The biotite alters easily, losing iron and magnesia and 
forming sericite and rutile. 

That quartz also alters to sericite is now well known. The thin 
sections of the Boulder rock show it developing abundantly along 
strain cracks and also in cavities corroded into the surface of the 
mass. Just what chemical reactions are involved is not certain. The 
quartz is soluble in waters containing alkaline carbonates, but the 
sericite is not. At the same time both potash and alumina occur in 
many natural hot waters of alkaline reaction, and the silica dissolved 
by the waters may at once unite with potash and alumina and form 
sericite. 

i Elemente del Gesteinslehre, Stuttgart, 1890, pp. 70, 7J, 



2-18 MINERAL VEIN FORMATION AT BOULDER HOT SPRINGS. 
ORIGIX OF THE YEIN-FORMIXG MATERIAL. 

It is evident from the foregoing reactions that the waters may derive 
their alkaline carbonate and silica from the leaching of the vein walls. 
If the hot spring waters contain CO, they will alter orthoclase and 
plagioclase. the resulting product being sericite, silica, and carbonate 
of lime, while sodic carbonate derived from both the soda-bearing 
orthoclase and the plagioclase (andesine) will he carried in solution. 

The altered rocks are all oxidized and show much red and yellow 
oxides of iron and of sericite. Iron pyrite was not found except in 
one thin section. This lack of pyrite is believed to he due to oxidation 
taking place near I lie surface, which acts upon the sulphureted hydro- 
gen of the hot-spring waters, and changes the pyrite to iron sulphate. 
The resulting materials would at once he neutralized by the alkaline 

carbonates of the waters, resulting in the bright-colored oxides of iron 
-ecu. Patches of hematite were also found in the red jasper, and as 
the distribution of the iron oxides through the hot-spring deposit indi- 
cates that it ha- been derived from pyrite, it seems evident thai the 
change has taken place since the sealing up of the fissures and the 
retreat of the waters to a lower level. This would explain also why 
so little sulphureted hydrogen occurs in the outflowing waters. In 
common \\ ith the pyrite formed by it in depth, and which it is believed 
exists in abundance in the altered wall rocks of the veins below, it has 
formed sulphuric acid by oxidation, and this ha- been neutralized by 
the carbonates of the waters, with the production of sodium sulphate 

and sesquioxide of iron. The overflow at the upper springs is not 
energetic enough to bring the waters to the surface with their normal 

deep-seated character. At the lower spring, near the hotel, the phe- 
nomena of rock alteration or mineral deposition can not be studied t<> 
advantage, owing to the boggy character of the ground about the 

spring. 

(.OLD AM) SIIiVEB < <>N I IN is OF Till! \ KINS. 

The mineral content- of the veins are insignificant from an economic 
point of view, though of much scientific interest, a- they prove that 
the fissure tilling constitutes true mineral veins. Assays made by 
('. E. Monroe for the Survej show the following results: 

I IZ. pi T lull 

White calcareoua vein filling { (ioM " " : ' 

ISilvcr 40 

Altered granite alongside vein / (, " lfl Trace 

(Silver 0.40 

"Jasperoid" vein filling / Gold Trace 

(Silver. 0.05 

Copper stains are prominenl in flat fractures of the altered granite 
exposed in the shafts, and specimen- of the led •• jasperoid" show 



WEBD.] 



THEoKV OF ORE DEPOSITION. 



249 



patches of crystalline specular hematite. Pyrite is seen in thin section, 
and the red hematite staining is in part derived from pyrite and not 
from altered ferromagnesian minerals. 

The solubility of gold in waters holding sodic carbonate and sulphur- 
eted hydrogen was established by Becker in his study of the quicksilver 
deposits of the Pacific slope. 1 As stated by him, these substances are 
common constituents of hot-spring waters, and the}' occur in the waters 
of the Boulder springs. The origin of the gold is believed to be the 
granite itself. The occurrence of the large ore deposits of the State 
in veins cutting the basic peripheral masses of granite batholiths is 
significant, however, as indicating that the veins have derived their 
precious-metal contents from the leaching of the basic border rocks. 

RECENT MOVEMENT OR FAULTING OF THE VEIN. 

The brecciated character of part of 
the hot-spring deposit shows that this 
vein filling has been broken by move- 
ment or faulting since its formation, 
and there is no reason to doubt that 
such movements are still in progress, 
and that crustal adjustment is still 
going on. Some emphasis is laid upon 
this fact, as it shows that a fissure 
may be completely filled, forming a 
vein, and that this vein may reopen 
and become brecciated by later move- 
ment. The specimens figured (PL 
XXXIV, A, and fig. 13) show the 
brecciation of the red jasperoid and 
its recementation by silica. 

THEORY OF ORE DEPOSITION 
IN MINERAL VEINS. 




[G. 13. — Diagram showing the red "jasper" 
deposit shattered by later movements 
along the vein and the fragments cemented 
by newly formed opaline silica and quartz. 
Drawn from nature. Shaded part is red 
jasper; white is chalcedony. 



The origin of the heat of the Boul- 
der hot springs is believed to be deep 
seated; it is probably connected with 
the rhyolite intrusions which formed 
the latest manifestation of volcanic activity in the region. These 
rhyolite rocks occur in dikes and irregular intruded masses rather 
commonly throughout the entire granite region. They also form 
large areas of extrusive rocks covering the granite. Although 
no rhyolite was found near the springs, the widespread occurrence 
of such intrusions indicates a general source of supply — a reser- 
voir of heated rock which may have supplied the heat of the present 
hot springs. The fact that fissures are still forming in this region 



1 Urology of the quicksilver do) msits of the 1'aci lie slope, liv ( ;>-orv.. 
Vol. XIII, 1888. 



. Becker: .lion. Q.S.Qeol. Survey, 



250 MINERAL VEIN FORMATION AT BOULDER HOT SPRINGS. 

.shows that meteoric waters could penetrate to a depth sufficient to 
become heated and rise again along trunk channels, such as those 
of the hot springs themselves. In other words, the springs owe 
their heat to the lingering traces of volcanic action of which the rhyo- 
lites are the main evidence. This theory, too. accords with the wide- 
spread occurrence of the jasper reefs, which indicates the former 
existence of hot springs over the region. 

It has long been believed by a majority of the students of ore 
deposits, and 1>\ most mining men. that such deposits are formed by 
hot waters ascending from unknown depths. Fora decade or two the 
advocates of the theory of ore deposition b\ descending waters or 
laterally moving currents obtained a qualified acceptance of their 
hypothesis, bul in recent years there has been a reaction, a return to 
the ascension theory. < >ne good result, however, of the discussion 
following the presentation of the theory of lateral secretion has been 
a general recognition of the fact that ore deposits are formed in many 
different ways. During recent years researches have demonstrated 
that opening- can net exisl in the rocks which compose the outer 
crusl of the earth at depths of 30,000 feet or more, and that, indeed, 
under certain condition-, they can not exisl at depths very much less 
than that. Observations made upon deeply buyied rocks brought to 

the surface l>\ uplift and erosion are in perfect accord with these 

deductions, and prove that the "unknown depths" from which ore 
deposits in waters are derived can not exceed these figures. In a 
geological Btudy of the hoi springs in the Yellowstone National l'ark 

and in adjacent parts of Montana the writer long ago became con- 
vinced that the source <>f the heat i- not truly profound, 1 but that the 
springs are of meteoric origin and form pari of the normal under 
ground circulating water of the region, heated by physical conditions 
giving it access to the ~till hot rocks beneath. It is not necessary, 
therefore, that the ascending hot waters which are commonly sup- 
posed to deposit ore- should come from very great depths. 

Assuming this to he true, it w ill probably be admitted, since heat 
and pressure facilitate solution, that hot waters circulating al consid- 
erable depths will dissolve ami take into solution various materials, 
metallic and otherwise, with which they come into contact. The 
capacity of the hot water to contain such substances in solution will 

depend upon heat and pressure. The water will take up the less 
readih soluble salts only while the condition- are favorable. With 
less heat and pressure the solution may become saturated for any one 
substance and. though -till holding it in solution, lie incapable of tak- 
ing up any more of that substance. In this unstable condition a 
slightly lessened temperature and heat would bring about precipitation. 
In an ideal hot spring meteoric waters, slowly traversing heated but 
solid igneous rocks, out of which they dissolve various substances, 

' Smithsonian report 1898, pp. 168-178; Schoi New York, Vol. XI, pp. 289 



weed.] THEORY OF ORE DEPOSITION. 251 

How toward the point of easiest escape, which is the hot spring fissure. 
For convenience we will assume this fissure to be straight, a thousand 
or two thousand feet deep, and the waters to move upward very slowby. 
In its lower part, as in the pores of the adjacent rocks, heat and pres- 
sure are very great and the waters arc not saturated, even for the most 
insoluble substances, and no minerals are deposited. Nearer the sur- 
face diminished heat and pressure make the water incapable of taking 
more of the less soluble materials in solution, forming what may be 
conveniently called the zone of saturation. Some salts, like alkaline 
sulphates, etc., are extremely soluble, and the point of saturation is 
scarcely ever reached in nature, even at the earth's surface. Others, 
like silica, may be present in such amount as to saturate the water, but 
the solution is clear until cooling and relief of pressure cause super- 
saturation and precipitation occurs; a case seen at the Opal and the 
Coral Springs of the Norris Geyser Basin, in the Yellowstone Park. 
Still higher in the Irypothetical hot-spring pipe diminished heat and 
pressure cause the separation out of the less soluble constituents, and 
for such materials this part of the tube is the zone of precipitation. 
It is well known that the metallic sulphides are soluble iti alkaline 
solutions under heat and pressure, but examples showing their deposi- 
tion by living hot springs are extremely rare. The more soluble sub- 
stances will be carried farther upward before precipitation, and one 
might even suppose, if the solubilities of the substances were suffi- 
ciently unlike, that zones would be formed each one consisting mainly 
of the particular substance thrown out by the change of pressure. 
This would produce an orderly distribution of the ores in a vertical 
direction. This, indeed, has been frequently observed. Chamberlin 
records it for the lead and zinc deposits of Wisconsin, and Rickard 1 for 
those of Colorado and elsewhere. In the writer's own experience the 
order appears to be galena on top, passing into highly zinciferous ores 
below, and this into low-grade pyrite. It is a common experience to 
find this association in silver-lead deposits in limestone. This would 
account also for impoverishment in depth and the passing into the 
ever-present and readity deposited silica. 

The conditions in a hot spring tube are admittedly those postulated, 
i. e., lessening heat and pressure as the surface is approached, and the 
assumptions made are natural ones. This, then, would explain why 
hot springs do not deposit metallic sulphides at the earjth's surface. 
Owing to their relative insolubility these are deposited (if present 
in the water) at depths below the surface. The Sulphur Bank 
quicksilver mines of California are examples. At the surface they 
showed only sulphur and no quicksilver. In depth quicksilver ores 
appeared. Were these springs to die out and degradation to remove 
the upper 200 feet of the ground, quicksilver veins would be exposed. 
It is probable that somewhat analogous conditions may exist at many 

i F. A. Ricard, Trans. Inst. Min. and Metal., London, Vol. VI, 1899, p. 196. 



252 MINERAL VEIN FORMATION AT BOULDER HOT SPRINGS. 

hot-spring localities and that if we could expose the lower part of the 
conduit we should find ore deposits. This is the theory which the 
writer at present holds as to the genesis of the silver-gold veins of 
Lump Gulch and other mining districts of Jefferson County, Montana, 
and which lie believes is a rational ascension theory. All secondary 
alterations are here excluded, these remarks applying only to the 
primary vein tilling. It is lateral secretion only in the very special 
and limited application of that term to the leaching of relatively deep- 
seated rocks and the gat lie! ing of such waters in a hot-spring conduit. 
The close resemblance in nature and occurrence of these Boulder 
hot-spring veins to the jasper reefs of Clancy. Lump Gulch, and 
many other mining districts in the granite area of Jefferson County 
has already been stated. It may he accepted as certain that they also 
owe their origin to hot springs and that the ore deposits of such \ eins 
were formed by hot waters. 

MICROSCOPIC PETROGRAPHY OP THE AXTERED ROCKS 

am> \i:i\ ni.i,i\(i. 

Mr. Waldemar Lindgren has kindly furnished the following notes 
upon the petrographic characters shown in thin sections of the rocks 
from this locality. 

nil mi BRED OR WIIK. 

The fresh granite of Boulder, Montana, i- related, as shown by .Mr. 
Weed, to quartz-monzonite. The rock consists of a medium-grained 
aggregate of quartz, orthoclase, plagioclase (predominantly andesine), 
brown biotite, and a little tilanite. A- secondary minerals a small 
amount of chlorite connected with biotite appear-, while sericite and 
muscoA ite are absent. Adjoining the \ ein this granite is altered to a 
reddish, crumbly rock, in which the biotite has disappeared and the 

feldspar is partly replace. I ly a Boft, grayish mass. Large quartz 
grain- remain in the rock, which i- porous bj inaiiv large spaces of 
dissolution. 

Aplite is also seen in thin sections and these show a scarcity of 
biotite, an absence of andesine, and a structure which appears more 
like a mosaic than the original idiomorphic structure of the quartz- 
monzonite. 

A considerable amount of orthoclase and quartz remains unaltered. 

even in the specimens t attacked bj the metasomatic processes. 

The altered rock contains abundanl spots and nests of fine-grained 
secondary aggregates, which appear between the grains and gradually 
corrode the adjoining priman constituents. .Many of these secondary 
it s appear in the middle of some grains of quartz and feldspar, 
and are gradually spreading outside. Near the secondary aggregates 
the quartz and feldspar are generally completely filled with irregular 
fluid inclusions, generally massed on planes of fracture, hut in these 



weed.] MICROSCOPIC PETROGRAPHY. 253 

inclusions no secondary minerals have separated out. Some aggregates 
in the rock appear, to judge from their structure, to replace biotite. 
Besides the later-described minerals they contain bunches of rutile 
needles. 

The secondary aggregates consist of : 

Sericite. — This mineral develops in places in unusually large foils, 
replacing orthoclase and, to some extent also, quartz; they are asso- 
ciated with the minerals described below. The larger part of the 
sericite appears, however, as bent, irregular fibers, which sometimes 
develop directly in the feldspars, or, again, are mixed with other 
secondary aggregates. 

Kaolinite. — This mineral is in some sections present in much larger 
quantities than the sericite, although in all of these rocks the two 
minerals occur together. The kaolinite forms an aggregate of minute 
scales of irregular outline, which presents very low colors of inter- 
ference and occasionally fibrous structure, as shown by the action on 
polarized light. The mineral occurs in large aggregates and can easily 
be distinguished from the sericite often embedded in it. Much more 
difficult is the distinction from the secondary quartz described below, 
and the study requires strong magnifying power. Kaolinite replaces 
the feldspar, orthoclase, or soda-lime feldspar, but it also distinctly 
forms from the quartz, and many grains of the latter may be seen in 
process of kaolinization. 

Fibrous silica. — Intimately mixed with the kaolinite are ver}^ irreg- 
ular grains and shreds of secondary quartz having a pronouncedly 
irregular fibrous structure. The mineral has a little higher double 
refraction, but somewhat lower refraction than the kaolinite. It is 
doubtless a peculiarly developed variety of chalcedony. 

Some fragments of aplite which are inclosed in a quartzose ground- 
mass, probably a consolidated and altered mud, present phenomena 
of replacement a little different from those described, inasmuch as 
the secondary silica predominates and the final product appears to 
tend toward a fine-grained jasperoid. The quartzose grains in these 
included fragments are notmuch altered, though considerably shattered. 
The orthoclase is opaque by minute inclusions and is also traversed 
by a network of veins of predominating secondary quartz, with some 
kaolinite and a very little sericite. The silica appears as minute quartz 
grains, not as chalcedony. This is not really a shattering and 
recementing, but a process of corrosion involving replacement cer- 
tainly takes place, by means of which the feldspar is silicified. 

THE JASPEROID. 

Many of the specimens consist of a reddish, very fine-grained chert 
or jasperoid, which is traversed by minute veinlets of quartz and stil- 
bite and which contains many small fragments of apparently clastic 
quartz grains. Under the microscope these grains are seen to be clearly 



254 MINERAL VEIN FORMATION AT BOULDER HOT SPRINGS. 

clastic and apparently not corroded or replaced. The principal mass 
is exceedingly line grained and contains many small inclusions of red 
oxide of iron as well as scattered aggregates of light-greenish serpenti- 
noid material. There are also a few small aggregates which unques- 
tionably consist of kaolinite. The prevailing mass appears between 
crossed nicols as a feebly double-retracting material with extinctions 
over large areas as a sort of shadowy network. The character of this 
mineral is in some doubt. It appears thai the specimen is largely com- 
posed of quartz or allied mineral, and the substance described may be 
a peculiar form of fibrous silica. Altogether it is probable that this 
fine-grained chert is not a product of replacement, bul a filling, or 
perhaps a partial replacement of finely comminuted material mixed 
with some coarser grains. 

The little veinlets traversing llf lock consist of a very line-grained 

mosaic of quartz. Along the walls small groups of stilbite crystals 
have grown, presumably prior to the later tilling. 

Till, i [LUNG. 

The filling consists of quartz, Btilbite, and calcite. As shown in 
many specimens, the following is the order of deposition: Next the 
wall .". nun. of granular stilbite are covered by l mm. of quartz crust. 

This, again, i- eov ered l>v 25 mm. of mixed zeolites and quartz, with a 

little calcite toward the interior. The centra] part appears to consist 
of some centimeters of cellular pseudomorphic quartz, accompanied 
by some calcite. On this framework of silica little warts of opal or 

hyalite are - times deposited. From all specimens it is apparent 

that subsequently to the deposition of the main mass of stilbite gran- 
ular calcite was formed, which again bas been dissolved and partly 

replaced by zeolites and quartz. 

Structun of filing. The main mass, consisting of zeolite and 
quartz, appears in thin section a- a network of prismatic crystals 
cemented by a mosaic <>f quartz grains. The prismatic crystals have 
very low refracting and birefracting power. The cleavage in one 
direction is excellently developed, with pearly luster on the face. 
The extinction- from the vertical axis range from to a maximum 
of l.". . In the >eetion> of the zone perpendicular to the base cleavage 
the extinction is . The character of the double refraction La nega- 
tive. From all these data the conclusion that the zeolite is stilbite 
may lie drawn with considerable confidence. One prism was found 
having an extinction of :\i . and another, also monoclinic or triclinic, 
in which the double refraction was of positive character. It i- thus 
possible that a few grains of different minerals, also zeolites, may he 
admixed with the main ma-- of stilbite. 

The coarsely granular calcite forming the later part of the tilling is 
characterized by a prevalence of spear-shaped grains and long, slender 



weed] MICROSCOPIC PETROGRAPHY. 255 

prisms. The triangular interstices are sometimes rilled with granular 
quartz. One section shows well the beginning of the alteration of 
this calcite to secondary quartz and stilbite. Along the contact lines 
of the long, slender, calcite prisms pseudomorphic action begins by 
deposition of a narrow rim of quartz mosaic. From this medium 
line long, slender crystals of stilbite project on both sides into the 
fresh calcite. Some crystals of the same mineral also develop in the 
calcite itself. By the gradual growth of this secondary mineral 
simultaneously with the dissolving of the calcite the primary aggregate 
of this mineral is converted into a cellular, honeycombed mass of 
quartz and stilbite. 



GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD 
INDIAN TERRITORY 

JiV 

JOSEPH A. TAFF and GEORGE J. ADAMS 



21 GEOL, PT 2 17 



CONTENTS. 



Page. 

Introduction 263 

Boundaries of the field 263 

Previous publications 263 

Maps 264 

Acknowledgments 265 

Topography 265 

General relations 265 

Ouachita Mountains region 266 

Arkansas Valley region 267 

Lowland plain 267 

Highland plain 268 

Ridges of the highland plain 268 

Mountains 270 

Stratigraphy 271 

General relations 271 

Character of sediments 272 

Atoka formation 273 

Hartshorne sandstone 274 

McAlester shale 275 

Savanna formation 276 

Boggy shale 278 

Structure 279 

General relations 279 

Folds 279 

Kiowa syncline 279 

Poteau syncline 280 

McAlester anticline 280 

Heavener anticline 281 

Sugarloaf syncline 282 

Cavanal syncline 282 

Brazil anticline 282 

Sansbois syncline 283 

Milton anticline 283 

Backbone anticline 283 

Bokoshe syncline 284 

Faults 284 

Choctaw fault 284 

Backbone fault 285 

Distribution of coal 285 

Hartshorne coals 287 

In the Hartshorne Basin 287 

In the Sansbois syncline 287 

In the Cavanal syncline 289 

259 



260 CONTENTS. 

Distribution of coal — Continued. 

Hartshorne coals — Continued. ,, 

Page. 

In the Heavener anticline 289 

In the Poteau syncline 290 

McAIester c< >al 291 

In the Sansboia syncline 



Tn the Brazil anticline . . 
In the Cavanal syncline. 
In the Poteau bj ocline. . 



291 

291 
291 
292 



Cavanal coal 

In the Cavanal syncline 292 

In the Sansbois bj acline ..,,.; 

Witteville coals ,„ )( 

In the Cavanal syncline 294 

In the Saneboifi syncline 295 

Tn the Poteau and Sugarloai synclinee 295 

Other coals in the eastern Choctaw coal field 295 

Mining development .,, )(i 

^Min iiiir districts 297 

< lowen district 



Wilburton districl 
Ola district 



21 -7 
297 



29S 

Panola district .„ )S 

Redoak district .„ IS 

Turkey Creek district 298 

299 



Fanshawe district 
Pocahontas <li>tri<t 



Wister districl .„,,, 



Mitchell Basin district 

Cavanal district 





foteau district 

Witteville ili>tri<-t :;m 

Maybern <li-trict 



301 

Jenson district . ;u i 

Panama district ■;,,., 

Pocola district ..,,., 

Tabular summary of mining operations 304 

Composition and adaptabilitj of coals :;i)( ; 

Analyses of coals .. (| - 

Methodsof sampling 31 q 

Bcation of coals oin 

Variation of coals . ;| , 



ILLUSTRATIONS. 



Page. 
Plate XXXV. Map of the Choctaw Nation, showing the southern limit of 

the coal field and the area surveyed 264 

XXXVI. Map of the Choctaw coal field, showing axes of the folds and 

crops of the principal coal beds 280 

XXXVII. Map of the Eastern Choctaw coal field, with five structure 

sections In pocket. 

Fig. 14. Vertical section of coal and associated rocks in the Hartshorne Basin, 

at the west end of Long Mountain 287 

15. Section across the Hartshorne Basin through Long Mountain 288 

16. Section through the mines at the west side of Wilburton 289 

17. Section of rocks at the Potter mine 290 

18. Section of coals and associated rocks in the Mitchell Basin 291 

19. Section of coal in the Cavanal mine 292 

20. Section of the Witteville coals and associated rocks at the Witteville 

mines 295 

261 



GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD, 
INDIAN TERRITORY. 



By Joseph A. Taff and George I. Adams. 



INTRODUCTION. 

Boundaries of the field. — The Eastern Choctaw coal field is the direct 
eastward continuation of the McAlester-Lehigh or Western Choctaw 
coal field, which was mapped and reported upon in the Nineteenth 
Annual Report of this Survey. It extends to the Arkansas-Indian 
Territory line, whence the same coal-bearing rocks continue down the 
Arkansas River Valley about 75 miles, to the eastern termination of 
the Arkansas coal field. The outcrop of the Hartshorne sandstone, as 
shown on the map, is the southern boundary of the Eastern Choctaw 
coal field. A short distance south of the outcrop of the Hartshorne 
sandstone a fault bearing nearly east and west separates the coal- 
bearing rocks on the north from the rocks on the south, in which no 
coal has been found in Indian Territory. The plane of this fault 
dips steeply away from the coal field, and the rocks south of it have 
ridden upward and over the rocks on the north side. The movement 
or displacement along this fault is estimated to be several thousand 
feet, so that the rocks on the south side now on a level and in contact 
with those on the north are the older. During the time of faulting 
or since it occurred the rocks on both sides of the fault have been 
reduced by erosion to the same plane. The northern limit of the field 
mapped and discussed in the following pages is not the natural limit of 
the productive or workable coals, but is arbitrarily drawn at the 
northern boundary of the area surveyed up to the present time. 

This part of the coal field, comprising an area of nearly 750 square 
miles, is the extreme southeastern part of the Coal Measures of Indian 
Territory, which have an area of nearly 20,000 square miles. The 
Indian Territory coal field connects that of Arkansas with the fields of 
Kansas, Missouri, and Iowa. 

Previous publications. — In 1890 Dr. H. M. Chance made a survey of 
the southern border of the Choctaw coal field from the region of Harts- 

263 



2<U GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

home to the Arkansas State line. 1 His paper is the first publication 
of any consequence concerning- the geology of this region. With his 
report there is a sketch map with sections showing quite accurately 
the location of the lowest and highest productive coals. The interme- 
diate and less profitable coals are briefly discussed in the text and are 
indicated in the section. 

In 1891 Mr. Robert T. Hill made a reconnaissance of the western 
part of the Choctaw coal field. 2 In his paper Mr. Hill discusses the 
structure, and locates on his reconnaissance maps the lowest pro- 
ductive coal considered by Dr. Chance. 

In 1895 Dr. J. .1. Stevenson also investigated the coal field across 
the southern part of the < !hoctaw Nation. :; In his publication he cor- 
relates the work done by Mr. Hill and Dr. Chance with Mr. Winslow's 
section of the same rocks in western Arkansas. 

In 1896 Dr. N. F. Drake made a general survey of oearly the entire 
coal field of Indian Territory. In his publication ' Dr. Drake maps the 
limits of the coal fields of Indian Territory, and shows a direct con- 
nection between those of Kansas and Arkansas. Although Dr. Drake's 
work was in the nature of a reconnaissance, he separated the Coal 
Measures into formations and showed the principal coal beds, with the 
general stratigraphy and structure. 

Maps. 'I'he ma].- accompanying this report are drawn from the 
surveys recentlymade by the United States Geological Survey. Quad- 
rangles of nearly the same size, hounded by degree and half-degree 
lines of longitude and latitude, each having an area of nearly 950 
square miles and including a portion of the Five Nationsofthe Indian 
Territory, have been surveyed and the maps are being drawn and 
engraved for publication. Neither corners nor lines of the quadran- 
gles are located upon the ground, and reference to the maps is oeces- 
sar\ tor their location. It will he observed that the townships are 
drawn in the correct relative positions i,, which they occur and that 
the exact elevations above sea level of the township corners are given. 
On the ground these township corners are located by iron posts, upon 
the caps of which are cul the numbers of the four adjoining townships, 
with the elevation of the bench mark above sea level as shown on the 
map. The section and quarter-section comers are located by stones 
or posts, near which trees are marked indicating the adjoining section. 

The map of the Choctaw Nation (PI. XXXV) is introduced to show 
the southern limit of the Choctaw coal field and the area covered h\ 

\ >n. I nst.Min.Eng., Vol. XVIII, 1890, pp c, .,; ,,, i 
•-Not.-onanTonnnNsanr i„ tem in Indian Territory \.,. Jour Sci 

3d series, Vol. XIJI, 1891, pp. Ul-124. 
'Trans. Now York Acad. Sci.. Vol. XV, W95, pp, , 
•A geological reconnaiasi fielda oi Indian Terrltory.by Noah Fields Drake: Proc 

Am. Philos.Soc., Vol. XXXVI, pp I2i ,, ., ,,, , IM „ ,,. rililhr , „ ,,„„,.„ j 

to Biology from the Hopkins Seaside Llbrm o] XIV, L898. 



U. S GEOLOGICAL SURVEY 



TWENTY-FIRST ANNUAL REPORT PART II PL XXXV 




MAP <>K Till-'. CHOCTAW NATION 
SHOWING THE SOUTHERN LOUT OF THE COAL FIELD AND AREASURVEYED 



.1. A.TAFF 



■.!> ,\I>XMS. 



TOPOGRAPHY. 265 



detailed surveys. On account of the small scale of this map. only the 
quadrangle boundaries, principal streams, railroads, and towns are 
shown. 

On the map (PI. XXXVI) drawn to show the structure and location 
of the principal coal beds the topography is omitted on account of the 
small scale of the map and in order not to obscure the structure. The 
quadrangles, township lines, railroads, and principal towns are shown, 
as aids to the location of the features of structure and of the crops of 
coal beds. This map includes, together with the map of the Eastern 
( 'hoctaw coal field, the area of the McAlester-Lehigh coal field reported 
upon in the Nineteenth Annual Report of the Survey, Part III. This 
combined map brings together in one view the structure of the entire 
southern part of the coal region of Indian Territory. 

The geologic map (PI. XXXVII, in pocket) includes parts of six 
quadrangles — the southern parts of the Fort Smith, Sallisaw. and 
Sansbois, separated by meridians i»4 : 30' and 95°, respectively, and 
lying north of latitude 35°; and the northern parts of the Poteau 
Mountain, Winding Stair, and Tuskahoma, in the same order south of 
latitude 35°. 

Acknowledgments. — The results brought out in this report are in 
part due to the services of Mr. G. B. Richardson, who assisted in the 
survey of the geology in the vicinity of Redoak. It is not possible to 
express the indebtedness of the Survey for the numerous courtesies 
extended by residents and by those who are interested in mining 
operations throughout the field. Without exception every request 
was granted and service was extended by the officials of the mining 
companies as far as was in their power. Thanks, however, should 
especially be extended to Mr. L. W. Bryan, United States mine 
inspector for Indian Territory, and to the superintendents of the mines 
and other officials of the many companies operating coal. 

TOPOGRAPHY. 
GENERAL RELATIONS. 

The surface configuration of the land is expressed on the geologic 
map by level or contour lines, each of which throughout its course 
indicates a definite elevation above the level of the sea. The vertical 
distance between the positions of an}' two contiguous contour lines is 
50 feet. To aid in determining the elevation of any contour, those at 
intervals of 250 feet, beginning at sea level, 'are made heavier and have 
numbers placed upon them showing their height above the sea. It- 
will be observed that these lines, besides indicating the elevation above 
sea, also show the positions and true outlines of mountains, hills, 
and valleys — in other words, the relief or configuration of the land. 



266 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

Besides indicating the relative positions of the mountains, hills, and 
valleys, the contour lines show the grade or slope of the land. Where 
the surface is steep the contour lines fall near together, and where it is 
nearly level they are widely separated. With the aid of the contour 
map a discussion of the topography may be understood as readily as 
if the country itself were in view. 

The configuration of the land in this region is a direct result of the 
wearing away of the rocks by rain and streams. This need not be 
explained, since any one in the country may see the rains wash the soil 
into rivulets, and the stream freshets carry it away as mud and sand 
toward the sea. The progress of this work is very slow, it is true, 
but it lias been going on for a long period of time. 

The positions and forms of the mountains, hills, and valley- have 
been determined chiefly by the structure of the rocks. A reference to 
the geologic ma]) will show that the upturned edges of the sandstones 
define the ridges and that all the mountains are located within the 
broad, -hallow synclines. 

The area included in the ma]) of the Eastern Choctaw coal field 
embraces a part of two topographic regions, one of which, the Ouachita 
Mountains region, begins at the southern border of the Choctaw coal 
held and coincides with the Ouachita Mountains, which bear west from 
Arkansas into the southern pari of the Choctaw Nation. Only a brief 
reference to this province will lie necessary. The other topographic 
province is to he known a- tin' Arkansas Valley region, which, as its 
name indicate-, lies along the Arkan-a- River between the Ozark 
Plateau on the north and the Ouachita Mountains on the south. Its 

structure, a- well as it- topography, is sufficiently distinct from either 
of the provinces which hound it to entitle it to a distinct name and 
separate discussion. 

OUACHITA MOUNTAINS REGION. 

The structure of this province, of which but a narrow strip i- shown 
on the map south of the Choctaw fault, i- characterized in Indian 
Territory by many narrow, closely pressed, and overturned fold-, 
which are broken in a great many places by faults. The fold- and 
principal faults are generally parallel, having an east-west hearing in 
the eastern part and a northeast-southwest hearing in the western 
part. Some of them are many miles long, hut the greater number are 
short and occur with lapping or imbricating ends. Thick and hard 
beds of sandstone and lime-tone separated by soft shales are upturned 
in these numerous fold-. The -hales have been worn down to low, 
nearly level valleys, while the sandstones and limestones remain in 
generally parallel, sharp-crested hill-, ridges, and mountain-. In the 
central part of the province the folds are widest and correspondingly 
broad, level valleys and high mountain ridges occur. 



TAFF AND ADAMS.] TOPOGRAPHY. 2()7 

ARKANSAS VALLEY REGION. 

This province blends with the prairie plains to the northwest. It is 
bounded upon the north by the foothills of the Boston Mountains, 
which form the southern limit of the Ozark Plateau. The transition 
is well marked, being a change from a nearly level plain to an elevated, 
dissected plateau. The southern limit in Indian Territory is not so 
clearly defined, since the east-west-trending ridges in the northern part 
of the Ouachita Mountains region are similar to man} r of the ridges 
found in the southern part of the Arkansas Valley region. The great 
fault above referred to defines approximately the dividing line between 
the topographic provinces. 

Although this fault passes from the hydrographic basin of the 
Arkansas River southwestward to the drainage of the Red River, a 
distance of nearly 120 miles, it is throughout its course in low and 
nearly level valleys. The formation lying along the fault upon the 
north side is composed of soft rocks and is worn down nearly to a level 
plain. On the divide between the waters of Fourche Maline and 
Brushy creeks the plain is so nearly level that it is difficult to discern 
the direction of the- slope. From this low divide the Fourche Maline 
flows eastward along the fault at a grade of less than 3 feet per mile. 
The Poteau River meets the Fourche Maline in this valley from the 
cast and flows northward at the same low grade, meandering widely in 
a broad, level valley. These valleys lying along the fault are parts of 
the low plain which extends throughout the Arkansas Valley region 
in Indian Territory and which is known here as the lowland plain. 

LOWLAND PLAIN. 

Wherever soft rucks occur, and in places where hard beds are steeply 
upturned in the anticlines, the surface has been reduced by erosion to 
nearly the same low level. This lowland plain extends around all the 
mountains and separates the residual ridges and hills of the highland. 

The smaller streams are adjusted to the smaller structural features 
to a considerable degree. They often parallel the monoclinal ridges, 
culling their channels along the strike and occupying the outcrops of 
the softer rocks. Such a stream is James Fork, flowing from east to 
west along the flank of the Backbone anticlinal region. Owl Creek 
and the lower portion of Brazil Creek bear a similar relation to the 
southward-dipping rocks in the broad ridge to the north of them and 
to the low ridges which are on the flanks of the Sansbois and Cavanal 
mountains. 

These low-level broadened valleys lying between the mountains 
grade insensibly northward into the greater valley of the Arkansas. 
The streams of the lowland are corrading their channels very little, 
and in general are sluggish and are bordered by wide flood plains 



268 GEOLOGY OF THE EASTEEN CHOCTAW COAL FIELD. 

which are very little below the general surface of the lowland plain. 
Poteau River, especially, has numerous meanders and old channels. 

Away from the flood plains of the streams, which are heavily 
timbered, there are small prairies that occupy a large part of the 
lowland plain. The surface «'f the prairie land is generally nearly 
flat, and in rainy season- very wet. As a result chiefly of this lack 
of drainage there is produced a peculiar hummocky surface. The 
hummocks are low mounds hut a lew feet in height, are oval or circu- 
lar in outline, and are separated or surrounded by level spaces. The 
soil of the hummocks i- a loose, sandy loam, while that id' the sur- 
rounding flat surfaces is a more dense clay or sandy clay soil. Usually 
a clump of hushes upon the hummocks has assisted in the accumula- 
tion of mold, thus making the soil more porous. Water passes 
through the looser -oil of the hummocksand collects on the surround- 
ing levels, where the soil is nearly impervious. There are doubtless 
a number of causes which have assisted in producing this peculiar 

hummocky form of the level land, but the principal one seems to he 

the oft-repeated and long-continued accumulation of water in the 
lower spaces, which dissolves away the more soluble elements of the 

-oil and at the same time make- itjnoiv compact. 

HIGHLAND PLAIN. 

A great number of ridges, hill-, and nearly level highlands rise 
from the lowland plain to elevations of nearly 800 feet above sea level. 
These crests, therefore, lie practically in a horizontal plane which is 
considered to have been the general level of the country in recent geo- 
logic times. The \alh\ - <,f the stream- lie below it. and above it rise 
the residuals of the mountain-, among which the Arkansas River drain- 
age flows. A few of these mountains have elevation- approximating 
the high lei el- attained by the principal ridges of the ( hiachita Moun- 
tain- and the Ozark Plateau. The Arkansas River sinks gradually 
deeper in thi- plain eastward from the border of the prairie plains. 
The residual elevated area- which form thi- highland plain of the 
Arkansas River Valley may lie described a- ridges, hill-, and mesas or 
table-lands. Those rising above this plain attain the dignity of moun- 
tain- and will he so described. 

Ridge8oft7u highland plain. The thicker and more resistant sand- 
stones which have been upturned at appreciable angles a- a result of 
folding stand out as ridges, \\ hich usually do not rise to heights of o\ er 
200 feet. Their crests are nearly level, often for long distances, and 
extend close to the flood plain- of the more prominent -t lea in-, whose 
channels cut across them. The ridges have generally a low slope on 
the side toward which the rocks dip. the other side, which exposes 

the edges of the beds, being usually precipitous and sometimes having 

dill's at the top. 



TAFF AND ADAMS.] HIGHLAND PLAIN. 269 

The arrangement and distribution of these ridges depend upon the 
geologic structure and the geographic distribution of the beds of sand- 
stone in the lower formations exposed in this region. In the Atoka 
formation the beds of sandstone are heaviest in the eastern part of the 
field, and the ridges formed by their outcrops swing in broad, elliptical 
curves, serving to illustrate upon the surface the great folds into which 
the strata have been thrown. 

Toward the west the sandstone beds disappear irregularly from the 
formation, and consequently the ridges diminish in number and impor- 
tance. In the northwestern part of the field, in the Backbone anti- 
clinal region, the rocks of the Atoka formation appear and form a 
number of sharp ridges, the most conspicuous of which is called the 
Devils Backbone. 

The ridge produced by the Hartshorne sandstone is the most promi- 
nent in the southern part of the coal field. . With the exception of 
occasional gaps, where it is cut by streams, it is continuous from 
Poteau River westward. Between Poteau River and Heavener it is 
lower than is usual elsewhere, and in places it has been worn down 
nearly to the level of the lowland plain. West of Heavener, where 
the sandstone crosses the axis of the Poteau syncline 1 , it becomes nearly 
horizontal, and forms a pointed, low table-land projecting to the banks 
of Poteau River. From the Kansas City, Pittsburg and Gulf Railroad 
eastward this ridge diminishes in elevation until it is lost in the valley 
of Sugar Creek, south of Poteau Mountain. 

Along the southern border of the area mapped as the McAlester shale 
there are a number of more or less persistent ridges or elongated hills. 
Although they are usually low and not easily traced, their arrangement 
indicates that there arc a number of thick sandstone beds in the forma- 
tion. The ridges are not well shown in the topograph y of the maps, since 
they are relatively low. In the northern part of the field the sandstone 
beds in the McAlester shale have changed in character, so that they 
produce more prominent ridges and hills. A conspicuous ridge, which 
in its middle portion takes on the structure of a mesa as a result of the 
lowering of the dip of the rocks, may be seen well defined on the map 
between Brazil and Milton. Where the dips are steep the ridge is 
sharp; as the dips become more nearly horizontal the form changes 
from that of a ridge to a mesa or table-land. 

The lower part of the Savanna formation consists of sandstone beds 
alternating with shales, and where they occur far out on the flanks of 
the mountains they produce ridges. The most notable of these occurs 
west of the towns of Cavanal and Poteau, north of Cavanal Mountain 
and at the eastern base of Sansbois Mountain. A remnant of the 
lowest sandstone in this formation caps the mesa just east of Cameron. 

Between the Backbone Ridge and others parallel with it north of 
Cavanal and Sansbois mountains and the Boston Mountains north of 



270 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

Arkansas River the surface is generally at a lower level. However, 
in areas of horizontal rocks there are remnants of flat-topped hills or 
mesas, some of which stand upon the edge of the flood plains of the 
river with their crests in the older plain. 

It is not now possible to discuss the history of this highland plain, 
since but a part of the held in which it occurs has been surveyed. 
There is, however, some evidence which indicates that in recent geo- 
logic time the surface of the region in which this highland plain occurs 
was move nearly level than at present, having been reduced to a surface 
of little relief, above which towered the mountains, as they do to-day 
above the summits of the ridges and the plateaus. The most apparent 
evidence of this former surface is to be seen in the almost uniformly 
level crests of the ridges and hills which lie in the highland peneplain. 
Surveys in the Coalgate, McAlester, and Canadian quadrangles, in the 
northwest part of the Choctaw Nation, have located the old course of 
a river which flowed in a wide, meandering, shallow channel but little 
below the level of the highland plain. This old channel has been traced 
southeastward from the Canadian River Valley, in the northwest cor- 
ner of the Choctaw Nation, across the drainage flowing into the Red 
River, and thence northeastward back to the Canadian River Valley, 
northeast of McAlester. In places the banks of this old channel may 
be recognized as low escarpments. Usually, however, the remnants 
of sand and gravid deposits now left upon the present divides are all 
that mark its location. Similar upland deposits of sand and gravel are 
found in the northeastern pari of the Choctaw Nation and in the south- 
eastern part of the Cherokee Nation, about LOO feet above the Arkansas 
River Valley. These deposits in places are 40 feet in thickness and 
more than 2 miles wide. It would naturally be cone bided that a broad 
and shallow meandering stream which deposited such quantities of fine 
sand and silt could have existed only in a nearly level plain. 

MOUNTAINS. 

The mountains of this coal field are all of the same type and have 
similar detail of surface features. They are all of synclinal structure, 
and the same formations occur in all four of the mountains in this field 
and in nearly the same relative position. It is explained later, in the 
discussion of the structure, that the outlines of these mountains conform 
to the forms of the synclines which they respectively occupy. Each of 
the various beds of hard and soft rock has its influence, where it out- 
crops, in forming particular features of the mountains. Thus it is 
that the rocks indicate the character of the mountains; and the form 
and features of the mountains in turn tell their story of the character 
of the rocks and of the geologic structure. 

The mountains are characterized by benches and terraces, which are 
formed by the eroded edges of alternate hard and soft strata that dip, 



TAFF AM. ADAMS.] STRATIGRAPHY. 271 

usually at a low angle, toward the centers of the masses. In the lower 
slopes tlic heavier beds of sandstone form encircling ridges. High up, 
where the dips are low, the}- project in abrupt benches, ledges, and 
cliffs, which are often impassable. The shales, falling away more 
rapidly, form the terraces and slopes between the benches and cliffs. 
The streams dissecting the mountains have cut deep trenches, and in 
places have separated the mountains into knobs and peaks, as in Cav- 
anal Mountain, or into a mass of high, irregular ridges, as in Sansbois 
Mountain. The sides of the mountains, knobs, peaks, or ridges, how- 
ever, all have the bench and terrace type of sculpture. 

STRATIGRAPHY. 

General relations. — The formations shown upon the map and dis- 
cussed in this report are of Upper Carboniferous age, as determined 
by both fossil shells and fossil plants contained in them. From the 
Hartshorne sandstone upward in the stratigraphic section the forma- 
tions are coal bearing. By the evidence of fossil plants occurring in 
the shales associated with the coal beds the Hartshorne or Grady coal 
is found to belong to the Lower Coal Measures, while the McAlester 
coal is classed with the Upper Coal Measures.' 

Beds of sandstone and shale in alternating strata occur in regular 
succession below the Hartshorne sandstone to a thickness of nearly 
7,000 feet. These rocks are a part of the Atoka formation. The 
other portion of the formation is partially concealed by the overthrust 
of older rocks from the south along the fault. The nature of this 
fault is explained later under the heading "Structure." While the 
occurrence of coal is not known in this formation, it has been reported 
by prospectors in Fourche Maline Valley, south of Wilburton. It 
is possible that workable coal may be found in it, since the whole 
formation lies within the Lower Coal Measures. The Atoka formation 
is considered in this report because of its possible economic importance 
and its structural and age relations to the coal-bearing rocks imme- 
diately above it. 

The rocks south of the fault line are not differentiated. They are 
older, but belong, in part at least, to the same geologic period as the 
rocks north of the fault. The former are thrown into close and gen- 
erally overturned folds and probably are much faulted, while the 
folds of the latter are wide and relatively flat" and shallow, as is illus- 
t rated in the maps and sections. 

The geology of the unmapped area upon the north side of the field 
and of a small part of the east end adjoining the Arkansas State line is 
not considered in this report, since the survey was not sufficient to 
differentiate the rocks. 

'Geology of the McAiester-Lehigh coal fleld, Indian Territory, by Joseph A. Taff, David White, and 

George H. Girty: Nineteenth Ann. Rept. 0. S. Geol. Survey, Part III, i>p. 186-466, 471. 



272 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

Character of sediments. — The beds of rock whose edges come to the 
surface in this coal field and arc discussed in this report arc sandstone, 
shale and coal. Shale succeeds sandstone and sandstone follows upon 
shale repeatedly, with many coal beds interspersed, until there is a 
thickness in all of nearly 1-2.700 feet. The lowest bed is in contact with 
the fault at the south side of the area mapped, and the highest bed is in 
the crest of Cavanal .Mountain (Section Gr— H, PL XXXVII). Farther 
west, beyond the region here discussed, sandstone and shale beds occur 
above these rocks to a thickness of many hundred feet; they doubtless 
once occurred here, but have been removed by the agencies of erosion. 
Through all these strata there is apparently a regular conformable 
succession, the beds being parallel, though crumpled or folded. This 
being true, there is but one interpretation of the manner of their 
formation, namely, that they were deposited in the sea or other bodies 
of water as the bottom continually but slowly sank. ( )tl shore, beneath 
the action of the waves, or in limited shallow basins where the water 
was not disturbed, the tine material was carried and deposited as 
mud and became shale. Near shore and in shallow active water sand 
was transported and laid down and finally became sandstone. In 

swamps and probably aear long stretches of shore vegetable matter 
accumulated, sinking down into a peaty mass. As the land subsided, 
this vegetable matter was submerged by the sea and covered by 

deposits of mini and Band, and after a long period of time became 
coal. Throughout all the formations occurring in this coal field there 
is a wonderful regularity in the physical appearance and composi- 
tion of the sandstones. Without exception they are all composed of 
finely divided material, no very coarse-grained or pebbly masses 
being observed. The character of the rocks themselves testifies to 
the assertions concerning the manner of their formation. In many 
of the sandstones in this field may bfi -ecu ripple marks and other 
evidences of the action of water in their deposition. In the shales 
there are thin sheets or lamina' of relatively coarse and tine substance, 
showing changes in the velocity and course of the current or change,-, 
in the source of material. In the coal may be seen the fibrous struc- 
ture of plants, and in the -hale in contact with the coal ferns and plant 
Stems are often found bearing all the detail of their original structural 
beauty. 

The rocks of this field all belong to the ( !oal Measures. West of it 
limestones which belong to the Lower Coal Measures occur below the 
Atoka formation. Fossils were not found in the highest rocks here, 
but in the westward extension of this field, in the northern part of the 
Choctaw Nation, still higher rocks are found which are included within 
the Upper Coal Measures. 

The division between the Upper and LowerCoal Measures, as deter- 
mined upon the evidence of fossil plants by Mr. David White, of this 



tafi ua> adams.] ATOKA FORMATION. 273 

Survey, is at some horizon in the strata between the Hartshorne and 
McAlester coal beds, presumably near the middle of the McAlester 
shale. 

Besides the remarkable thickness of the rocks as a whole, and the 
even texture of the sandstones, there is the not less remarkable great 
extension from east to west of many of the relatively thin sandstone 
beds throughout the field. The, Hartshorne sandstone is an example. 
This bed or collection of thin beds of sandstone, not more than 200 
feel thick, extends westward from the Arkansas State line completely 
across the Choctaw Nation, a distance of nearly 200 miles, without any 
known break in outcrop. 

Atoka formation. — This formation occurs with irregular width 
along the southern side of the Eastern Choctaw coal field. Near the 
State line, on the southeastern side of the field, the formation as far as 
exposed aggregates a thickness of between 6,000 and 7,000 feet. At 
intervals of from 1,000 to 1,200 feet in these shales there are four 
groups of sandstone strata, each of which is nearly 100 feet thick. 

As the formation is traced westward it is seen that the lower tw T o 
groups of sandstone are cut out by the fault. The upper sandstone 
beds may be traced farther west, to near the central part of the field, 
but beyond that they are not known to occur. It is presumed, there- 
fore, that they are lenticular in form and are limited in their extent 
from east to west beneath the surface as well as in outcrop. Near the 
western end of this coal field, in the Boiling Springs anticline, the 
formation is exposed to an estimated thickness of nearly 3,000 feet, 
and in this exposure no rock of consequence except shales was observed. 
South of the eastern end of the Hartshorne Basin, in the southwestern 
corner of the field, not more than 300 feet of the formation is exposed 
between the Hartshorne sandstones and the fault line. 

The sandstone beds are brown or light gray and are often thin and 
slabby, being separated by shaly layers. The shales are very rarely 
exposed. Where exposed they are seen to be usually bluish clay 
shales with occasional ferruginous ironstone concretions. Each group 
of sandstone, where not worn down by active stream erosion, forms 
a low and nearly level-crested ridge, and the shales are worn down 
to level \ alleys and plains. 

The extraordinary thickness of this formation may appear peculiar 
and may be questioned by some who would suggest that there may be 
duplication in thickness of rocks by faulting. The best estimate of 
the thickness of the formation was made in the anticline west of Poteau 
Mountain, where faulting to any appreciable extent would be readily 
detected. Section (i II, crossing the anticl ine referred to, as well as 
the rocks upon the south along the fault line, illustrates the relative 
positions of the sandstones and shales. 

The irregularity in width and form of the outcrop of this formation 
21 GEOL, i-r 2 --IS 



274 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

is due to the northward overthrust along the great fault which borders 
the held on the south side and to the irregular folds which limit its 
outcrop on the north. 

Ifartshorne sandstone. — An aggregation of brown, gray, and usually 
thin-bedded sandstones which locally become shaly constitutes this 
formation. The upper beds are in places thick, and even massive, 
while the lower ones are generally thin and grade into shale toward 
the base. In places the sandstone beds are thin and shaly throughout; 
at others — for instance, in the railroad cut south of Petros switch, on 
the Kansas City, Pittsburg and Gulf Railroad -the sandstone is sepa- 
rated into three beds, with shale intervals, each containing a thin coal 
seam. In this railroad cut the following section is exposed: 

Section in mi u.iir Petros switch, Indian Territory. 

Feet. 

Shaly sandstone, tup do1 seen, exposed 8 

Shale with two thin bands of bituminous matter 20 

Disintegrated coal and bituminous shale 8 

Shaly sandstone 5 

Shales 10 

Sandst- .ne 30 

Shale, light bine 10 

Disintegrated coal and shale t; 

Bine shale, base not exposed 15 

The thickness of this sandstone could not be accurately determined. 
By measuring the dip and horizontal distance across the outcrops at 
numerous places estimates were made, which varied from loo feet to 
a little less than 200 feet. 

The rlartshorne sandstone forms a ridge which has a generally level 
crest 50 to 200 feet in height, except where it is cut bya water gap or 
is locally worn l>y streams which in recent times have been diverted 
from their course. 

This formation shows at the surface in this field in two main lines 
of outcrop. The most extensive is along the southern side of the Held. 
and is rudely parallel to the fault. The line of outcrop enters this field 
from the west and curves around the end of the McAlester anticline 
west of Wilburton. From Wilburton it trends nearly due east for 
a distance of about 40 miles, where, in the vicinity of Heavener, it 
turns south and then west in the form of a hook around the east end 
of the Heavener anticlinal dome. From the south side of this dome 
the outcrop of the sandstone bears eastward to and beyond the State 
line, on the southern side of the Poteau syncline. 

There are two coal beds associated with the rlartshorne sandstone, 
known as the upper and lower rlartshorne coals. The upper lied is 
above the sandstone and is separated from it by a thin bed of shale, 
which is variable in thickness. Locally this coal bed rests almost upon 
the sandstone. It properly belongs i M and at the base of the McAlester 



tapf ixd idams.] MCALESTER SHALE. 275 

shale, which overlies the Hartshorne sandstone. The contact line at 
the top of the Hartshorne sandstone is drawn approximately upon the 
crop of this eoal. The lower Hartshorne eoal bed is separated from 
the upper by nearly 50 feet of sandstone and shaly strata. The occur- 
rence and character of these eoal beds are described further on. under 
the headings ••Distribution of eoal," '"Mining- development." and 
••( iomposition and adaptability of coals." 

McAlester shale.- This formation occupies the largest area of any 
occurring in this coal field, and its coal beds are the most numerous 
and the most economically important. On account of the soft nature 
of its beds, the surface is worn down nearly to a level, and the gener- 
ally low dips of its rocks permit successful mining of its eoal beds in 
relatively large areas. 

The contact line at the base of the McAlester shale is approximately 
upon the upper bed of the Hartshorne coal. The sandstone and the 
coals associated with it have been located by prospects at intervals 
throughout the field. The parting line at the top of the McAlester 
shale, between it and the Savanna formation, was not located with the 
same ease and precision as that at the base. There is no coal known 
at or near the upper limit of the McAlester shale, the prospecting of 
which would assist in the location of the contact. Where the sand- 
stones of the overlying formation occur in steep slopes, as they do 
along the south base of Sansbois Mountain north of Brazil Creek, and 
also north of Fourche Maline and west of Redoak, the talus from them 
often conceals the lower beds, so that the contact in many places can 
be only approximately located. Around the east end of Sansbois 
Mountain and completely around Cavanal Mountain, however, the 
parting line is so far removed from the mountain that it may be read- 
ily and quite accurately determined. The dips of the rocks are low, 
and each important sandstone bed marks a well-defined ridge or ter- 
race which may lie traced with ease. 

The McAlester shale is estimated to range from 2,000 to 2,500 feet 
in thickness. The measurement in the western part of the field gives 
nearly 2,000 feet and in the eastern part about 2,500 feet of strata. 
Since the dips are variable both along and across the strike, the esti- 
mates for thickness are only roughly approximate. 

Several sandstone beds occur in the McAlester shale, but none are 
continuous, SO tar as can be determined, throughout the held. As a 
whole, however, they become generally thicker and more prominent at 
the surface from west to east. Many of the sandstone beds can he 
traced several miles, but none can he accurately mapped, even within 
the limits of their occurrence. These sandstones are generally thin 
bedded, though locally they are massive and form ridges. Like most 
other sandstones in the ( \>al Measures in this held, they are tine grained 
in texture and brown in color, and are usually hard, hut are sometimes 



276 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

friable, when they are worn down with the shales so that their edges 
are concealed. Where the sandstone beds are thickest and are not cut 
down by streams they form low, nearly level-topped ridges. Such 
ridges occur between Redoak and Wilburton, in the vicinity of Fan- 
shawe. and between Wister and Howe, north of the Choctaw, Oklahoma 
and Gulf Railroad. In Brazil Creek Valley north of Redoak some 
upper layers of these sandstones are exposed on the low areh of the 
Brazil anticline and produce low. irregular hills. North of Brazil post- 
office and between Cameron and Shady Point some of the sandstone 
beds are locally much increased in thickness. North of Brazil, espe- 
cially, one of the sandstones occurs in massive beds, making a wide 
ridge. The prominence of this ridge, however, is due in part to the 
structure, the sandstone being nearly horizontal. 

The Bhalesof tin- formation probably aggregate more than live times 
the thickness of the sandstones, though their natural exposure can 
randy be found. Hie occurrence andareal extent of these shales may 
be determined with comparative ease and accuracy by studying the soil 
and the surface configuration of the country. On careful examination 
of the surface it will he found that the most insignificant sandstone lied 
makes it- presence known by a ridge or rising ground or by its unde- 
COmposed talus or debris. The soil of the country above the shale 
outside of the flood plains of the streams has been produced by decom- 
position of the rock in place, so thai the soil becomes an index to the 
nature of the rocks beneath. < mtside of the immediate stream \alle\ s 
the shales produce a (lav loam and usually form prairie lands. The 
shale of the McAlester formation, as shown by the prospect drill and 

other artificial means, as well as bj occasi il natural exposures by 

streams, is generally some shade of blue, although black bituminous 
shales are commonly associated with the coal >c:niis. The shales are 
always laminated or stratified in thin beds, and \ ar\ from bed to bed in 
the quantity of sandy material they contain. 

ddie coal in the McAlester shale aggregates 8 to 1 1 feet in thickness 
and includes three know n workable beds, if the upper I Iartshorne coal. 

which is practically u] tin contact of the base, be included. This 

Hartshorne coal has a thickness ranging between land 8 feet. The 
other two beds occur in shale 10 to 60 feet apart vertically and from 
600 to 700 feet below the top of the formation. Each of these coal beds 
varies in thickness between -± and '.'> U-rl. They occur in the horizon 
of the McAlester coal, though it is not known positively whether either 
of them is a continuation of the McAlester bed. The character of these 
coal beds is discussed in detail in the following pages under the head- 
ings "' Distribution of coal."* •Mining development," and "Composi 
tion and adaptability of coals." 

Savanna formation.- This formation is limited to and forms the 
lower portions of the mountains in this coal field. It outcrops in the 



tapp and abase.] SAVANNA FORMATION. 277 

lower slopes and extends from the base well up toward the crests 
of Sansbois, Poteau, and Sugarloaf mountains. In Cavanal Moun- 
tain the formation is limited to the foothills and encircling ridges 
extending from Redoak around the mountain nearly to Cameron. In 
each instance the formation lies high in the synclines or structural 
basins occupied by these mountains. Indeed, the mountains owe their 
existence to the presence of the sandstones of this and the succeeding 
formation. By an examination of the topography of the mountains, 
as represented on the map. the location and presence of each of the 
prominent sandstones of this formation may be seen in their encir- 
cling projecting edges as so many giant dishes or basins, of gradually 
smaller proportions, stacked one upon another. 

The Savanna formation contains three prominent divisions or col- 
lections of sandstone beds, having a thickness of from 100 to about 200 
feet each and separated by masses of shale and thin sandstone, with 
two known workable coal beds. The upper division of this series of 
sandstones is the thickest, being nearly 200 feet thick; its upper strata 
are locally massive. Toward the base the strata are seen to become 
gradually thinner and change to shaly sandstone and shale. As may 
be seen by reference to the map, this sandstone has the most marked 
effect upon the topography where its ridge encircles the mountains 
immediately below the upper contact of the formation. The medial 
bed is the next in importance and thickness and is also a prominent 
ridge maker. In section this sandstone bed resembles the uppermost 
one, the thicker ledges being above. Downward the beds grade into 
shaly sandstone and then into shales. The lowest sandstone, while 
neither so thick in section nor so prominent as a ridge-forming rock, 
is not less important, from the fact that it is associated with a promi- 
nent coal bed. 

The shales of the Savanna formation are separated into two divisions 
by the medial sandstone bed. The upper of these varies in thickness 
from 450 to 530 feet, while the lower division ranges from 300 to 450 
feet. 

The shales of this formation are as a whole more sandy than the 
shales of the formation below, though they are friable and disinte- 
grate readily, forming valleys and level stretches of country. 

Estimates of the thickness of this formation vary from 1,200 to 
1,500 feet. It appears to grow thicker from the west toward the east. 
The lowest estimate was made near the west end, in Sansbois Mountain, 
and the highest near the east end, in Poteau Mountain. It will be 
observed by reference to the map that the dips of the rock vary 
between 5° and 70°. The variation in dip is along as well as across 
the strike. Under these conditions an approximate estimate of any 
section may vary as much as 100 feet from the actual thickness. 

There are two coal beds occurring within the limits of the Savanna 



278 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

formation, one in the lower part, almost immediately below the medial 
sandstone division, and the other very near the top of the upper sand- 
stone division and practically at the top of the formation. 

Boggy shale. — To those acquainted with the surface rock of Cava- 
nal and Sansbois mountains the word ''shale' 1 doubtless would not 
seem to be appropriately applied to this formation, because of tin- 
great mass of sandstone bowlders and talus known to occur in many 
places on its upper slopes. In spite of the apparent prominence of 
the sandstone, it makes relatively a very small part of the formation 
when compared to the shale. The sandstone strata altogether will not 
much exceed 100 feet, while there is nearly 2,000 feet of shale in 
Cavanal Mountain, where the formation has its greatest thickness in 
this field. Excepting one mass of sandstone, which occurs about -loo 
feet below the crestof Cavanal Mountain, the beds very much resemble 
those of the formations below in character and composition. They are 
chiefly thin bedded, brown in color, and of fine texture. The single 
sandstone referred to is generally massive and has a thickness of nearly 
100 feet. In places it IS white or a light shade of pink, and resembles 
very much a consolidated deposit of pure sand. The shale, as in other 
formations in this field, is rarely well exposed. In the mountains 
it is usually concealed by sandstone talus and debris. Immediately 

below the massive sandstone referred to there is about 4oo feet of even- 
textured blue clay shale. This section is exposed at the west end of 
the main peak of Cavanal Mountain. The lower part of the Boggy 
shale as well as that above the main sandstone i-. on the whole, more 
sandy, as shaly sandstone and sandy shale are interst rat died with the 
clay shale. Exposures of this shale are very limited in extent. As in 
the lower formations, the determination of the character of the shaly 
beds i- a matter of interpretation from surface indications of soil 
and disintegrated rock. 

Chiefly because of the structure this formation occurs in four 
separate areas in this field, viz. in Sansbois. Cavanal, Poteau. and 
Sugarloaf mountains. In Sansbois Mountain the remnant IS about 
1,600 feet thick from the base of the shale to the crest of the moun- 
tain. In Cavanal Mountain the section is estimated to be about 2,300 
feet thick. In Poteau and Sugarloaf mountains remnants from 500 
to 600 feet thick remain and form their tops. 

In the northwestern part of the Choctaw Nation the Boggy shale is 
estimated to be nearly 3,000 feet thick, and it is therefore presumed 
that 500 t<> 7"" feet of it has been removed from above the crest of 
Cavanal Mountain. 

One coal bed is known in the Boggy shale. This occurs about 200 
feet above its base. It is mined at the east end and upon the north 
side of Cavanal Mountain and varies between 3 and 4 feet in thick- 
ness. The occurrence of the coal is known by prospects practically 



i mi vm. . m.a.ms.] STRUCTURE. 279 

around Cavanal Mountain for a distance of nearly 30 miles. The 
presence of this coal in Sansbois, Poteau, or Sugarloaf mountains has 
not been determined. 

STRUCTURE. 

GENERAL RELATIONS. 

The type of structure of the Choctaw coal field is limited on the 
south side approximately to the occurrence of the coal-bearing rocks. 
It is characterized by relatively short, shallow, and wide lapping- folds. 
The synclines or basins on the whole are wider and shallower than are 
the anticlines or upward-arching folds. This variation may not seem 
apparent by casual reference to the map and sections on PI. XXXVII, 
since the mountains rest in and are formed by the downward-bending 
strata and the rocks in the arches are worn down to plains and valleys. 
The section on the line G— H, PI. XXXVI, illustrates this general 
characteristic of the folding. 

The anticlines near the south side of the field generally are not 
symmetrical. The strata upon the north dip at steeper angles than 
those upon the south. In one instance an anticlinal fold is overturned, 
so that the rocks on both sides dip in the same direction. This being 
true, the case would be reversed in the synclines, and the rocks have 
steeper dips on the south side of the folds. 

The intensity of the folding decreases from south to north or north- 
west in the Choctaw coal Held. Near the faulted district upon the 
south the folds are relatively deep and in places overturned, as 
explained. Northward, toward the interior, the folds decrease until 
they become wide, shallow undulations. Still farther northwest, yet 
within the Indian Territory coal field, folds disappear and the rocks 
maintain regular low northwest dips. 

On the map of the Choctaw coal field (PI. XXXVI) lines are drawn 
upon the axes or centers of the folds as far as the geologic survey, 
has been carried. The thickness of the lines indicate the relative 
magnitude of the folds. The crops of the known workable coal beds 
also are indicated by dot and short dash lines. 



Kiowa synclme. — This is a long synclinal fold which extends from 
near Gowen, on the western side of this held, to the southwestern end 
of the Choctaw coal field, west of Lehigh. The location of the axis of 
this fold is shown on PI. XXXVI. The syncline is flat and basin- 
like or spoon-like at each end and is broad and deep near tin 1 center, in 
the vicinity of Kiowa. The east end is known locally as the liarts- 
horne Basin, because of the extensive mining operations in it at 
Hartshorne and Gowen, and because it is surrounded by elevated sand- 



280 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

stone ridges. Fig-. 15 (p. 288) is a cross section of this basin a little 
east of the center. This section, drawn on the natural scale, shows it 
to be about 4 miles wide and 600 feet dee]) at this point from the sur- 
face down to the coal and sandstone which form its rim. 

The surface basin in the end of this syncline is exceptional and is 
opposite in character to that of the Poteau syncline, its counterpart in 
the east end of this field, and to others in this region of synclinal 
mountains and anticlinal basins or plains. The cause of this exceptional 
feature is that the rocks, with the exception of a few remnants of 
sandstone capping the mesas and knobs, are all shale or thin sandy 
beds, which are easily worn down to plains or valleys by erosion. The 
sandstones of the ridges forming the west side of the basin and those 
capping the mesas and knobs are the same, and once extended over the 
basin, forming an elevated laud similar to the west end of Sansbois 
Mountain. As soon as the watercourses found their way through the 
hard sandstones the wearing of the soft shales was more rapid, and the 
hills, protected by the sandstone on their crests, were gradually reduced 
until we have the presenl small remnants of tlat-topped hills in the 
basin. 

Poteau syncline. This is a long synclinal fold which stretches for 
more than loo miles along the south side of the Arkansas coal field and 
extends into Indian Territory for a distance of L2 or 15 miles. It is the 
counterpart of the Kiowa syncline. which ends in the Hartshorne Basin. 
Its axis curves northward and ends in the form of a spoon or canoe. 
The Hartshorne sandstone and shale beds occur here, forming a small 
basin at the wot end of Poteau Mountain, known locally as the Mitchell 
Basin. Shale and sandstone beds lying beneath the Hartshorne sand- 
stone are also brought up by the syncline, and they may be seen in 
the ridges curving successively around in the syncline for a distance 
of L0 miles \\e>t of Mitchell Basin and south of the mouth of the 
Fourche Maline. With the exception of the west end, this syncline 
is occupied by mountains, which rise to various altitudes, but continue 
practically as far as the syncline is known. 

M< . [lest* r anticlint . This anticline enters the held in Gaines Creek 
Valley, north of the Hartshorne Basin, and ends as a complete fold 
between the east end of this basin and Wilburton. The north limb of 
the anticline, however, continues eastward through the south side of 
this part of the coal field and becomes the north limb or side of the 
Heavener anticline, which lies immediately north of the Poteau syncline. 
The south limb of the McAlester anticline, between the Hartshorne 
and Mitchell basins, is concealed by the overthrust from the south side 
of the Choctaw fault. By overlooking this loss of a part of the anti- 
cline by concealment, the McAlester and Heavener anticlines would be 
considered as one fold. The original condition of the structure on the 
south between the ends of the two anticlines is concealed by the fault, 



U. S. GEOLOGICAL SURVEY 




STRUCTURE OF THE CHOCTAW COALFIELD 
INDIAN TERRITORY 

SHOWING AXES OF FOLDS AND CROPS OF PRINCIPAL, COAL FIELDS 

By Joseph A.Taff 
1900 




TWENTY-FIRST ANNUAL REPORT PART || PL XXXVI 




TACT AND ADAM8.] FOLDS. 281 

however, and ran not be known, and hence they are regarded as inde- 
pendent structures. 

The westward extension of the axis of this anticline passes through 
Cherryvale, from which place it curves northward through McAlester. 
Its exact location is shown on PI. XXXVI. 

The fold is not symmetrical. The rocks upon the north side have 
Steeper dips than those upon the south side, and in places they are 
overturned and faulted. 

A peculiar feature of this fold occurs east of Boiling Spring Creek, 
near the western border of this part of the field, which may be explained 
by reference to the Hartshorne sandstone. At the edge of the field as 
mapped, the Hartshorne sandstone, on the northern limb of the anti- 
cline, dips nearly 35°. At the head of Boiling Spring Creek the dip 
increases to 50°; then for some 3 miles farther east the rocks turn 
almost upon edge. Beyond this toward Wilburton the same bed curves 
toward the south, dipping as low as 10°, and thus forming the abrupt 
termination of a branch or part of the McAlester anticline, with its 
axis pitching almost directly downward at the end. The main axis of 
the McAlester anticline is considered to bear eastward beneath the 
Choctaw fault south of Wilburton, though the rocks on the south side 
are concealed in the level plain. 

ILiirrn, r anticline. — This fold is peculiar both in its form of 
development and in its bearing or course. From near the mouth of 
Fourche Maline its axis rises rapidly eastward into a high arch and as 
abruptly descends within a range of 6 miles southwest of Howe. 
Should the beds of sandstone which have been worn away and whose 
edges now crop out in the plain around the elliptical border of this 
dome-like fold he restored, they would form a mountain more than a 
mile high, *> miles long, and 3 miles wide. The bearing of the axis in 
this fold is a little south of east and almost directly in line with that 
of the Poteau syncline, against which it abuts. 

On the northeastern side of the Heavener anticline an anticlinal fold, 
which may he considered as a branch of the Heavener anticline, bears 
northeastward through the vicinity of Howe. From the location of 
Howe, nearly upon its axis, this anticline is known as the Howe anti- 
cline. A peculiar relation of the Howe to the Heavener anticline is that 
their axes do not join, yet the folds are not separated bj T any indication 
even of a syncline. It will be observed by reference to the map that 
the crop of the Hartshorne sandstone southwest of Howe does not bear 
any indication of the effect of a branch fold. The next sandstone above 
the Hartshorne, however, diverges from the Heavener anticline near 
Poteau River and bears northeastward beyond Howe, where it crosses 
the axis of the Howe anticline and turns southward in the Poteau syn- 
cline. Between Howe and Monroe the Howe anticline divides into two 
folds, one of which bears due east between Poteau and Sugarloaf moun- 



282 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

tains, while the other turns north between Sugarloaf and Cavanal 
mountains and then east into Arkansas, north of Sugarloaf Mountain. 
Both branches of this fold are wide and flat. The valleys occupied by 
the Howe anticline are eroded in McAlester shale. The grades of the 
streams are very low and the valleys are practically level planes stretch- 
ing between the mountains from base to base. The economic bearing 
of this structure and topography will be brought out under the heading 
"Distribution of coal." 

Sugarloaf syncline. — This is a shallow trough which enters the 
Choctaw coal field from Arkansas between the two branches of the 
Howe anticline and is occupied by Sugarloaf Mountain, from which it 
derives its name. At the State line this fold is not more than 6 miles 
wide, and the locks are nearly horizontal, except those forming the 
outer rim at the north and south bases of the mountains. 

Cavanal syncline.— This is a wide, canoe-like trough, with narrowly 
contracted and shallow ends. The axis of the fold is in the form of an 
obtuse or flattened S. The west end joins the Sansbois syncline west 
of Redoak and bears due east about LO miles; then it turns northward 
25° and continues 25 miles through Cavanal Mountain to Cameron. 
From this point the bearing again becomes nearly east and so con- 
tinues into Arkansas. The structure of this syncline is illustrated by 
the three sections E— F, G— H, and I— J, PI. XXXVII. The first and 
last of these sections cross the fold near the west and east ends, respec- 
tively, and show the narrow and shallow character of the fold, while 
section Gr — H illustrates the extreme width and depth of the trough 
near its center. The outcrop of the formations also shows the form 
and extent of the basin. The base of the Savanna formation lies suf- 
ficiently near the border of the basin to indicate its bearing and form. 
Its successive hard and soft beds, forming concentric ridges and val- 
leys or benches and terrace- around Cavanal Mountain, will illustrate 
the details of structure. 

The adaptability of this structure to successful mining of the sev- 
eral workable beds of coal which crop around the border and in the 
interior of the basin will lie brought out in discussing the distribution 
of coals. 

Brazil anticline. — This is a low fold on which Brazil Creek Hows 
and from which it is named. This anticline separates the Cavanal and 
Sansbois synclines, and its axis is nearly parallel with that of the 
former. 

• The axis rises at an a nole of 15° in the side of Sansbois Mountain 
at the head of Brazil Creek, bears eastward, and then northeastward, 
parallel with the course of the creek. In the vicinity of Walls the 
axis pitches downward at a low angle, but rises again opposite the east 
end of Sansbois Mountain. From this point it bears more eastward 
north of Brazil post-office, where it joins the Buck Creek anticline. 



TAFF AND . U.AM- 1 FOLDS. 283 

The depression in the axis of this anticline opposite the cast end of 
Sansbois Mountain is a shallow cross syncline rising and then descend- 
ing from the Sansbois to the Cavanal synclinal basin. 

Sanxbo!* syncline. — This is a relatively long, shallow, and inter- 
rupted basin which extends eastward through Sansbois Mountain 
from the vicinity of Krebs, in the western part of the Choctaw coal 
field. In the western half of the syncline the rocks upon the south 
side arc steeply upturned and locally faulted, while, upon the north 
side the dips are so low that the synclinal structure is not easily per- 
ceived. From near the head of Fourche Maline to the east end of 
Sansbois Mountain the syncline becomes more symmetrical, the dips 
upon the north and south sides being nearly the same. Between the 
sources of Fourche Maline and Brazil creeks the geologic structure' is 
undulating and irregular. While the general form of the syncline 
is preserved, yet the rocks, especially on the south side, are variable 
in bearing of strike and degree of dip. This variability is due to the 
entrance of both the Brazil anticline and the Cavanal syncline into the 
south side of the Sansbois syncline. The interruption of the peculiar 
structure in the east end of the McAlester anticline between Boiling 
Spring and Fourche Maline creeks also causes local steep dips on the 
south side of the Sansbois syncline. From the source of Brazil Creek 
eastward the dips of the rocks are regular upon both the north and 
south sides of the synclines and are about 10°. 

From the east end of Sansbois Mountain this syncline contracts 
rapidly and rises to a narrow and shallow end in the highlands ?, 
miles south of Bokoshe. 

It will be observed by reference to the map (PI. XXXVII) that the 
axis of this syncline bears nearly due east from its west end near 
Krebs to a point opposite the west end of Brazil anticline, where the 
bearing changes to N. 70° E. and continues thus to its east end. 

MH/on anticline.— This anticline is a narrow and low fold lying 
next north of the Sansbois syncline and is named from the town of 
Milton, which is nearly upon its axis. It bears nearly east-northeast 
from its west end near McAlester to Bokoshe, where it separates into 
two folds, the southernmost of which is known as the Backbone anti- 
cline and has a bearing nearly due east. The northernmost branch of 
the fold bears northeast and lies north of the Bokoshe syncline. which 
separates the two divisions of the Milton anticline. This north branch 
of the Milton anticline is known as the Redland anticline, from the 
town of this name located nearly upon its axis, where the Kansas City, 
Pittsburg and Gulf Railroad crosses the Arkansas River. North of the 
east end of Sansbois Mountain the Milton anticline rises high enough 
to expose rocks below the lowest coal near its axis. 

Backbone anticline — The Backbone anticline is the fold which is 
broken by the Backbone fault, It is joined at the west end by the 
Milton and Brazil anticlines, as explained above. It is narrow and 



284 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

flat in the western part. The rocks upon either side dip at angles of 
from 5° to 10°, while near the axis the beds are almost horizontal. 
This anticline becomes wider and higher eastward, the dips upon the 
south side especially changing from 10 c to 25°. Where the axis 
crosses Poteau River the Backbone fault becomes prominent and con- 
ceals much of the north limb of the told. Though this fault extends 
through the central part of the fold and increases in magnitude east- 
ward to the State line, it does not completely obliterate the structure 
of the fold. As is explained in the discussion of the Backbone fault, 
the rocks upon the north side have low dips northward, while those 
upon the other side dip at very much steeper angles southward. 

Bokosht syndiru . As indicated above, this syncline lies between two 
branches of the Milton anticline, viz. the Backbone and the Redland 
anticlines. It is a relatively wide and flat basin running nearly east 
northeasl from the town of Bokoshe at the west end toward the State 
line -, ,iith of Fori Smith. Around the west end of this syncline the 
rocks dip in toward the axis at nearly In . As the same beds are fol- 
lowed eastward alone- the rim of the basin the dips gradually decrease 
until they become nearly horizontal, thus forming a Hat and shallow 
trough extending in width from the Backbone fault to the Arkansas 
River. Only the southwestern part of this fold is shown within the 
limits of the geologic map (PI. XXXVII). The axis of the fold as far 
as known, however, may lie -ecu upon the structure sections accom- 
panying the map. PI. XXXVI. 



Faults of the rocks in Indian Territory, a- far a- has been observed, 
are of one type thrust fault-. 

Prior to the occurrence of fault- of this type the rocks are usually 
thrown into folds by forces that are considered to bear in a horizontal 
direction. If , for reasons which often can not lie determined, the 
forces producing the folding be concentrated alone- a certain fold and 
become greater than the rocks can resist, a faulting of the beds is pro- 
duced, generally parallel with the folding, and the strata upon one side 
are thrust along the fault plane beyond those of the other side. 

The sections accompanying the geologic map (PL XXXVII) illus- 
trate the type- of fold- and faults found in the coal field. 

Choctaw fault. -This fault extends from the Indian Territory- 
Arkansas line west and -outhwe-t more than LOO miles, to the southern 
limit of the Indian Territory coal field. It separates this coal field 
from the older rocks of the Ouachita Mountain region. Prior to the 
faulting the rock- lying to the south of the ( hoetaw fault were closely 
folded, and in many iiistane.- the fold- were overturned toward the 
north. Then, as the pressure which produced the folding continued, 
the strata broke parallel to the folds and the rockfi 14)011 the south 



taki .'am. adams.] DISTRIBUTION OF COAL. 285 

side of the fracture were pushed upward and oxer those upon the 
north side. 

The vertical displacement of the Choctaw fault increases westward 
from a few hundred feet at the Arkansas line to several thousand feet 
at the western border of this field. 

Backbone fault. — The faults within the Coal Measures rocks are of 
limited extent, only one of any importance being - known within the east- 
ern Choctaw coal field. This is the Backbone fault, which crosses the 
Arkansas line upon the north side of Backbone Ridge, in T. X.. R. 
27 E. It extends in a westerly direction, as may he seen by reference 
to the map, for a distance of about 15 miles, where it dies out or is 
lost in the axis of the Backbone anticline. The Backbone fault is an 
overthrust from the south and is in this respect similar in nature to 
the great fault on the south side of the field. 

The vertical displacement of the rocks by this fault can not be accu- 
rately estimated, for the reason that the rocks in contact with the fault 
upon the north side can not be correlated with the strata upon the south 
side. The Hackett or Panama coal, which occurs south of the fault, is 
the lowest coal known in Indian Territory. Should the Bonanza coal, 
which occurs near the fault upon the north side, prove to be the same 
as the Hackett coal, the vertical displacement of the rocks due to this 
fault would be not less than 2,000 feet. Should the Bonanza coal be 
higher in the series than the Hackett coal the faulting would prove to 
be relatively gi'eater. As the fault line is traced westward it is seen 
that lower rocks successively crop out on the north side and higher 
beds are found in contact with them on the south. Thus the displace- 
ment of the beds decreases westward, until west of Poteau River it is 
but a few hundred feet. 

DISTRIBUTION OF COAL. 

Seven workable beds of coal are known in the eastern Choctaw coal 
field. They occur in four different formations, from the top of the 
Hartshorne sandstone, which is the lowest coal-bearing rock known in 
Indian Territory, upward to the lower part of the Boggy shale. The 
thickness of rock between the lowest and highest of these coals is 
estimated to be nearly 3,600 feet. Besides these coal beds, which are 
profitably worked, there are a number of others that are thin and have 
been located, chiefly by prospect drill, in various parts of the McAlester 
shale and Savanna sandstone. 

A knowledge of the geologic structure of the rocks in which coal 
beds occur and of the combined effects of structure and erosion on the 
topography or surface configuration of the land is necessary to the 
most successful economic prospecting and exploitation of the coal. 
Except to test the thickness and quality of a particular coal bed, the 
drill need not be called into use in a coal field of this nature. All the 



286 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

known coal beds are associated with sandstone beds of considerable 
persistency, which make their presence and location known by more or 
less elevated hills and ridges. When the interval between such sand- 
stone and coal beds is once established, the crop of the coal may be 
located as rapidly as the sandstone ridge or outcrop can be traversed. 
The dip of the sandstone may be determined at almost any point by 
measurements on its outcropping ledges. The coal beds, on the con- 
trary, usually lying in shale, have their edges worn down and concealed 
by soil and rock debris. The sandstone and coal near at hand remain 
nearly parallel. The distance of the coal outcrop from that of the 
sandstone can be readily estimated when the dip is known. The 
steeper the dip the nearer together will be the edges of the beds at the 
surface. The position of tin 1 crop of a coal heel being known, a knowl- 
edge of the grade and approximate depth beneath the surface through- 
out its area of occurrence is dependent entirely upon a knowledge of 
the structure. With such knowledge the availability of the. coal for 
mining, according to its inclination and depth beneath the surface, and 
the area of coal which may be successfully mined may be known, and 
a proper estimate may be made for the necessary mining plant and 
facilities for transportation of the coal. The proper method of min- 
ing in a particular locality can he best determined by a study of the 
structural features of that region. 

The occurrence and character of coal in this field are known only so 
far as it nas been prospected or mined. Experience has taught that 
beds of coal, like beds of any other rock, vary in thickness and char- 
acter from place to place. Thick beds of coal are known to become 
too thin to be successfully mined within the range of the working of 
a single mine. A lied of good quality in some instances changes within 
a short distance to a bony shale, or shaly beds enter it, so that it is 
worthless. It has been found, however, that the horizons or strati- 
graphic positions of the thicker coal beds are usually persistent — that 
is. wherever a particular coal horizon as established in this Held has 
been examined, coal has been found, though it may vary in thick- 
ness, texture, and quality. 

In this discussion of the distribution of coal, its horizon or its known 
stratigraphic position and its availability and area are considered, and 
it remains for the prospector and miner to determine its thickness and 
quality. 

It should also be borne in mind that the name of each coal bed should 
not cany with it the idea of exact correlation through the coal field. 
Each coal horizon as named has heen traced across the field by the aid 
of the outcrops of associated rocks. Most of the beds have been pros- 
pected through a large part of the held by prospectors using the drop 
auger and drill, yet the absolute continuity of a particular bed is known 
only when mines have been connected by gangways, or test pits by 
strippings. 



:AFK AM) Al'AMv | 



DISTRIBUTION OF COAL. 



287 



HARTSHORNE COALS. 



71 Shall 



These coals arc so named because of their early and most successful 
mining at the town of Hartshorne, just west of this Held, and because 
of their association with the Hartshorne sandstone. 

The Hartshorne coals, of which there are two in this held, occur in 
the upper part and at the top of the Hartshorne sandstone. This 
sandstone has been described under 
the heading "Stratigraphy," and 
its outcrop in the held is indicated 
by the map (PI. XXXVI). 

In the Hartshorne Basin. — Only 
the lower coal in this basin is of 
workable thickness. The vertical 
section of the rocks of this basin 
(fig. 14) shows the relative position 
and thickness of the Hartshorne 
coals. Near the center of the basin 
the lower coal bed is 3 feet 10 
inches thick by the drill record. 
Thesamecoal,workedattheGowen 
mine No. 3, in the east end of the 
basin, varies from 3 feet tj inches to 
5 feet in thickness. That which is 
considered to be the upper Harts- 
horne coal is -4 feet thick, hut is 
shaly and worthless. Fig. 15 is a 
section across the basin, drawn to 
natural scale, and illustrates the 
structure. At its center the Harts- 
horne coal is about 600fee1 beneath 
the surface. The axis pitches from 
the cast end nearly westward and 
at a low angle for a distance of 2 
miles, where it becomes flat, and so 
continues almost to the west end of 
the basin. From the ( Joweu mine 
the main entry inclines westward 
at a low grade in the axis of the syncline, and from (lie sides the coal 
is brought in by gravity and easy hauling. 

The area of the Hartshorne coal in the basin within the limits of the 
area mapped is about 5 square miles. 

/// ///, Sansbois syncline. In the south side of the Sansbois syncline 
the Hartshorne coals crop from the western border of the area mapped 
nearly to Redoak, a distance of 23 miles. A> far as is known, both 



Shah-, - - . . . . " 



Coal and shale, 17". 
Sandstone and sandy sli 

Shale and coal, 1G"." 

Shale, 'J'. 

Coal and shale, -i'. 

Sandstone and sandy sh 



Fl(i. 1 I.— Verticil] section of coal 

rocks in the Hartshorne Baa 
end "i Long Mountain. 



288 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

beds occur iii this sync-line. In the mining districts of Wilburton, 
Ola and Panola, both coal beds arc present in workable thickness, 
and they probably maintain their character throughout the entire 
syneline. They are separated by -±4 feet of sandstone and shale, and 




Fig. 15. — Section across the Hartshoi 

6, lower Hartshorne coal; c, upper Hartshorn 



Igb Long Mrmntiiin. 
oal. Horizontal and 



Hartshorne 
cal Bcale th< 



both may be operated by one hoisting plant from either a shaft or a 
slope. 

From the western border of the field to Fourche Maline Valley, a 
distance of 8 miles, the structure is probably not favorable for exten- 
sive and successful mining of the coal. Throughout this distance the 
rorks dip from 35 to 85 N.. and it is possible thai local faults occur 
in the rocks which have the steepesl inclination. The strike of these 
faults would follow approximately the strike of the rocks and could 
not be readily detected at the surface. 

In the Fourche Maline Valley, where the creek enters the plain from 
Sansbois Mountain, there is a local basin-like structure-. The Harts- 
borne sandstone ami coal change in strike from east to south, and then 
farther on toward Wilburton gradually change to nearly east again. 
With this change of bearing from easl to south, the rock changes in 
dip from near 50 to as low as lo , and then to -J.", near Wilburton. 
From Wilburton eastward the structure is regular, with dips toward 

the north. Along the crop of the coal the dip ranges fr 25 to 35 . 

while from the crop inward toward the axis of the syneline the dip 
decreases gradually to LO within a distance of a mile. At the base of 
Sansbois Mountain the Hartshorne coals are nearly 2,000 feet beneath 
the surface, as is illustrated in the section (' I). PI. XXXVII. drawn 
through the Wilburton mines. The quality of the coals which are 
mined at Wilburton is indicated by analyses in the table on page •'!<»>. 
It is that of a rather highl) bituminous coal, and differs but little 
from the coal mined at Hartshorne. The area of the coal which may 
he mined at depth- less than 1,000 feet beneath the surface in the 
south side of the Sansbois s\ ncline is nearly 15 square miles. 

The coal bed known as the Panama coal, considered to be in the 
same horizon as the Hartshorne beds, crops in the north side of the 
Sansbois syneline, dipping south. The correlation of these two coal 
horizons is based chiefly upon the determination that each is the low- 



HARTSHORNE COALS 



289 



est coal in the scries of coal-bearing rocks, the one in the faulted 
Backbone anticline, and the other in the faulted anticline on the south- 
ern side of the Choctaw coal field. Each occurs in the same relative 
position beneath the base of the McAlester shale and at the top of a 
sandstone of considerable importance, which in both cases is consid- 
ered to be the Hartshorne sandstone. On the north side of the Sans- 
bois syncline this coal is in places interrupted by shale, but is generally 
of workable thickness and of splendid bituminous and semibituminous 
quality. The dip of this bed varies from less than 10° to not exceed- 
ing 15 , SO far as known. Its area in the north side of the syncline 
has not been surveyed except on the northeast side of Sansbois 
Mountain. 

Tn the Cavanul xijiK-line. — Here likewise the Hartshorne sandstone 
occurs in both the south and north sides, but is of such depth in the 
fold that it does not pass in outcrop around its ends. Instead, it is 
tangent to the sides of the elliptical fold, and its outcrop curves south- 
ward around the east end of the Heavener anticline south of Howe 
Station, and then eastward into Arkansas, 
in the south side of the Poteau syncline. 
On the north side of the fold the outcrop 
continues from the end of the Sansbois 
syncline nearly due east into Arkansas. 
The structure of the rocks in this syncline 
is shown in section G— H, PI. XXXVII, 
and the position of the Hartshorne coal in 
the fold is at the top of the Hartshorne 
sandstone. The dip at the outcrop on the 
south side of the syncline ranges from 20° to 35°. In the north side 
it is L0 to i:» . The dip gradually decreases to L5 on the south side 
and 10° on the north side of the syncline at the top of the McAlester 
shale, where the coal is nearly 2,000 feet beneath the surface. In the 
south side of the syncline nearly 25 square miles may be mined at a 
depth of less than 1,000 feet, and on the north side nearly the same 
amount of coal is available within the same depth. 

In the south side of the field, between Redoak and Howe, both of 
the Hartshorne coal beds are present. They have been opened only 
in prospects, and the thickness and quality appear but little changed 
from those of the same coal beds mined at Wilburton. 

The Panama coal, in the north side of this syncline, especially in the 
Panama mine, is of higher grade than either of the Hartshorne coals 
in the south side of the syncline, as above described. It is classed as 
a semibituminous coal, is low in water, sulphur, and ash, and, as shown 
by laboratory coking tests, will produce a good grade of coke. 

/// tin Heavener anticline. — The dips of the Hartshorne coals along 
their outcrop eastward from the vicinity <>(' Pocahontas around the 
21 <;eol, pt2 L9 



Fig. 1G. — Section through mines 

the west side of Wilburton. 



290 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 




east end of the anticline change gradually from 40° to less than 10°. 
Beyond the outcrops of the coals, however, toward the north and 
northeast, the rocks are subject to different conditions of structure, 
which affect the economic importance of the 
coal. From the outcrop of the coal between 
Pocahontas and Poteau River the dip of the 
coals decreases northward at a low rate. 
From the outcrop between Poteau River and 
Heavener the dip decreases at a greater rate. 
In see. 2, T. 5 N., R. 25 E., for instance, the 
coals dip 10° at the outcrop. From this 
locality northeastward toward Howe and 
along the axis of the Howe anticline the dip 
of the coal becomes lowest, giving a rela- 
,. tively wide area in which these coals maybe 
mined. Fig. IT illustrates a section of the 
rocks, including the llartshorne coal, at the 
1 'otter n line, about 1 mile southwest of Howe 
Station. 

In tli. Poteau syncline. — The Mitchell 
'" Basin, south and southeast of Heavener, is 
. the depressed and flattened end of the Poteau 
syncline. It has been named for the pros- 
pector of the Choctaw. Oklahoma and Gulf Railroad Company, which 
lias leased and prospected this part of the held. In the northwest and 
wes< side- of this basin the coals dip southeast and east at 5° and less. 
From the west and along the Boutb side the dip gradually increases 
from less than ."> to 25 within '1 miles. 
The area of coal that ina\ lie successfully 

mined under existing conditions is nearly :; 
square miles. 

From the Mitchell Basill eastward to the 
State line, the crop of the coal lies at the 
base of Poteau Mountain. The dip through 
this course varies hut little from 25 N. 

The nu»t successful mining of the coal 
south of Poteau Mountain will he by slope. 
and necessarily hut small areas of the coal 
can he taken by the mining methods now 
employed in this field. 

In the south side of the ( 'hoctaw coal field 
from Pocahontas to the State line but one of the llartshorne coals has 
been exploited to any extent. It is considered that the lowest coal is 
mined at Potter and in the south side of the Mitchell Basin southeast 



Ion of rot 
Potter mine. 




Black shale, ■'■"'. 



Fig. 18.— Section <>f coals and asso- 
ciated rorksin the Mitchell Basin, 



TAFF AND ADAMS.] DISTRIBUTION OF COAL. 291 

of Heavener. Numerous bore holes have been sunk in the Mitchell 
Basin, which show the position of the Hartshorne beds and others of 
small extent. The section of the rocks here is illustrated in fig. 18. 

McALESTER COAL. 

There are two beds of coal within the McAlester shale in this held 
which occur in the stratigraphic position of the McAlester coal as it 
is known in the Dow, Alderson, Krebs, and McAlester districts, in 
the western part of the Choctaw coal field. These two coals arc sepa- 
rated here by about 60 feet of shale, and lie from 600 to 800 feet below 
the top of the formation. Below the coal there are a number of sand- 
stone beds which together make low ridges or hills, and which are 
excellent horizon markers for determining the position of the coal. 
The dip of the sandstone through the south side of the field is regular 
and toward the north, and when the position of the coal and its rela- 
tion to the sandstone is determined, as -it is at the Redoak, Turkey 
Creek, and Fanshawe mines, it may readily be traced throughout its 
occurrence. 

/// the Sansboix syncllne. — From the south sides of the Sansbois and 
Cavanal s}mclines the McAlester coal beds crop in the low and nearly 
level plain, almost parallel with the Hartshorne coal and sandstone, 
which occur below and to the south. They have not been mined, and 
have been prospected but little west of Redoak, hence the thickness 
and character of the coals are not known. 

In the Brazil anticline. — Brazil Creek flows in the center of the 
Brazil anticline from its source to the vicinity of Walls post-office, its 
valley being wide and flat. Several hundred feet of the upper part of 
the McAlester shale are exposed in the sides and bottom of the valley. 
Rocks in the horizon of the McAlester coal bed occur in the bottom 
of the creek valley, and several exposures of coal occur in the bed of 
Brazil Creek. One coal bed 18 inches thick has been mined for local 
use in Brazil Creek, at the mouth of Jefferson Creek, in the NE. j sec. 
10, T. 6 N., R. 22 E. Other outcrops of coal in this horizon occur in 
Brazil Creek north of Redoak. 

As far as known, these coal beds are not of sufficient thickness to be 
mined successfully at the present time. The rocks have low dips 
toward the north and south in the north and south sides of the valley, 
respectively. Thus conditions are favorable for successful operation 
of mines should coals of workable thickness be found. 

In the Cura nal syncli nr. — From Redoak to the Wister district the 
Mc A lester coal has been prospected and located at a number of places, 
and has been mined at Redoak, Turkey Creek, and Fanshawe. The 
cross section through Redoak (tig. 19) illustrates the structure and 
positions of the coals. From Redoak to a point opposite the aban- 




292 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

doned mines at Pocahontas the coals nop on the south side of the 
Choctaw, Oklahoma and Gulf Railroad. Throughout this course the 
dip is about 10° N. The crop lies south of Wister, in the valley of 
Mountain Creek. From near the mouth of Mountain Creek east of 
Wister the crop of the coal turns from 
aie with sheii bed ii i cast to northeast, into the flood plain of 

if coal. ' 

, al u , Poteau River. In the nearly level valley 

invariable shale parting. f Poteau River the dips are low toward 
the northwest, hence the crop is irregular 
and can he located only l>y prospect 'mil;'. 
Rocks in the horizon of the McAlestercoal 
Outcrop in the northwestern side of the 
Fig. i9.-Section .»f coal in the Cav- Cavanal syncline from the State line. 2£ 
'' "'""' '"' , ' !m """ miles south of Jenson, westward toward 
Shady Point. A coal bed has been pros- 
pected in the horizon of this coal about -J miles west of Cameron. 
Beyond tlii- prospeci toward the west the coal is not known north of 
( lavanal ami Sansbois mountains. Its horizon, however, may he located 
with tail- accuracy by taking into consideration the associated sand- 
stone lied-, which usually outcrop in L'idges and hills of greater or 
less relief. 

In tin Poteau syncline. The McAlestercoal horizon occurs at the, 
base of Poteau Mountain, dipping about 20 NW. on the south side, 
and nearly L0 S. on the north side. Around the west base of the 
mountain the dip i> usually less than ."i E. The thickness and quality 
of this coal in the Poteau s\ ocline are not known, it having been pros- 
pected but little and not at all developed. 

Likewise little is known of the McAlester coal in the Sugarloaf 

syncline in Sugarloaf Mountain. Some prospecting has been done 
near the horizon of the McAlester coal in the northwestern base of 
the mountain, but it bas not been exploited except for local purposes. 

CAVANAL COAL. 

lull,, Cavanal syncline. In the Cavanal syncline this coal is con- 
fined to Cavanal Mountain. It crops a little more than Mo feet strat- 
igraphically beneath the series of sandstone beds which make a line 
of prominent ridges surrounding the base of the mountain. The 
prospects U miles north of and at Poteau Station, the mines north of 
Cavanal Station, and those 3 miles west of Wister are located upon 
this coal. The contour lines on the map show the ridge made by the 
sandstone lying above and to the north and west of the mines and 
prospects referred to. From the mine west of Wister the horizon of 
this coal strikes nearly due wesl through sees, -j'.i and ."»<). T. «i N., K. 
24 E.. sees. 35 to 30, inclusive. T. <; X.. I J. 23 E., and in sees. 25 and 26, 



TAFF A.M. ADAMS.] CAVANAL COAL. 293 

T. 6 X., R. 22 E. In sec -21, T. 6 N.. R. 22 E., the strike curves 
north and then northeast beneath the escarpment of a high ridge. 
The position of this ridge, as may be seen upon the map, bears north- 
east and east around the west and north sides of Cavanal Mountain. 
In the north base of Cavanal Mountain the ridge above the coal is 
generally worn down, but the sandstone ledges outcrop in man} r places, 
and from these the crop of the coal may be easily located. 

The Cavanal coal, as far as known, is 3 feet to 3 feet 6 inches thick, 
LS well situated, and structurally disposed for mining. This coal dips 
beneath Cavanal Mountain at an angle varying from 6° to 20°. The 
lowest dip is on the southeast side, between Wister and Poteau Station. 
From Wister westward to Fanshawe the dip gradually increases from 
10° to nearly 20°. Beyond Fanshawe and upon the north side of the 
mountain it is nearty 10°. 

From the crop of the Cavanal coal inward toward the mountain the 
dip changes but little as a rule for a distance of between 2 and 3 miles. 
Considering the surface to be level and the dip of the rock to be 10°, 
the coal would descend at the rate of nearly 140 feet for each thousand 
feet of horizontal distance. The area of the coal in the syncline to a 
depth of 1,000 feet beneath the crop is nearly 05 square miles. 

The proximate analysis given in the table on page 308 is of the coal 
from the Cavanal mine, three-quarters of a mile north of Cavanal 
Station. It indicates that the coal is above the average of bituminous 
grade. The relatively high percentage of sulphur, however, is in the 
way of its successful use for cooking and some other purposes. 

In the Sansbois syncline. — As far as the survey has been carried, the 
Cavanal coal has not been prospected in this syncline. A coal bed of 
workable thickness in the stratigraphic position of the Cavanal coal 
crops out in a branch of Fourche Maline Creek, nearly -1 miles north 
of Wilburton. 

From the head of Brazil ( Jreek eastward the horizon of Cavanal coal 
gradually descends from the lower slope of Sansbois Mountain into 
the foothills which surround the base at the east end. The rocks at 
the horizon of the Cavanal coal in this portion of Sansbois Mountain 
dip beneath the mountain at angles varying from 10° to 20°. From 
the west end of Brazil Creek Valley westwa'-d to the border of this, 
tield the crop of the Cavanal coal lies in the steep lower slopes of 
Sansbois Mountain, dipping north. On account of the steep slope and 
the presence of bowlders and rock detritus, the sandstone near the coal. 
as well as that of higher beds, either outcrops as benches or as cliffs 
(>!■ the edges are concealed in the mountain side. In thespurof Sans- 
bois Mountain northwest of Redoak and in the high knob northeast 
of the same point the rocks in the horizon of this coal dip inward from 
the sides atangles of '■) and less. On the strike of the coal in the south 
side of Sansbois Mountain the dip of the rocks increases from 10 in 



294 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

the vicinity of Redoak to 30° in Fourche Maline Creek. From Fourche 
Maline Creek westward for 3 miles '.he dip increases from 30° to 70°, 
and then decreases rapidly to 30° again, and so continues to the western 
border of this field. 

WITTEVILLE COALS. 

There are two beds of coal separated by about 250 feet of shale and 
sandstone, which will he known as the Witteville coal beds, from the 
mines upon them at Witteville, in the east end of Cavanal Mountain. 

The upper Witteville coal is :'> feet L0 inches thick, separated into 
two nearly equal benches by a thin parting of shale. This coal has been 
mined at intervals since L894, and is delivered to the main line of the 
St. Louis and San Francisco Railroad at l'oteau Station over a .branch 
road belonging to the mining company. 

The lower Witteville coal is I feet 8 inches thick, and is separated 
into three benches by two variable bands of bone and carbonaceous 
-hale. It has been opened for exploitation on the crop at the tipple 

from which the coal from the upper mine is discharged for shipment. 

The lower coal occurs at the top of the Savanna formation, while the. 
upper bed is in the lower part of the Boggy shale, about son feet and 
l.iioo f,. r t. respectively, above the Cavanal coal. 

The quality of the Witteville coal, as expressed by the proximate 
analysis in the table on page :'><>*. IS nearly the same in all respects as that 
of the Cavanal coal, the percentages of volatile matter, carbon, and 
sulphur being a fraction higher, and the ash a little more than 1 per 

cent Less. 

/// tfi,' Cavanal syncline. The Witteville coal beds are not known in 
this field outside the Cavanal syncline. The lower Witteville coal being 
at the top of the Savanna formation, its approximate crop may be 
located by reference to I he contact between the Savanna and Boggy 
formations a- outlined on the ma]). 

The crop of the upper Witteville coal being 250 feet above the base 
of the Boggy -hale, it may be located approximately by reference to the 

Structure of the associated rocks in the syncline and the contact between 
the Savanna and Boggy formations. Where the slope of the mountain 
i- steep, a- at the Witteville mine, the crops of the coals will fall near 
together. At other place-, as upon the northwest and southeast sides 
of the syncline, where the surface is nearly level, the crops will be 
more widely separated. The dip of the rocks at the crop of the coal 
around Cavanal Mountain varies from 6 to 1<> . The dip becomes 
rapidly lower from the crop of the coal toward the center or axis of the 
syncline. and toward the mountain, so that relatively large areas may 
be mined by -lopes. In the more level areas in the vicinity of Kennady 
and north of Potato Peaks still larger area- may be worked by shaft. 



WITTEVILLE COALS. 



295 







Shale 
Coal 



Section G —II on the map (PL XXXVII) illustrates the structure, and 
fig. 20 gives a vertical column of the coal and rocks of Cavanal Moun- 
tain. In the section across the syncline the coals do not descend more 
than 1,000 feet beneath the level of their crops. From a shaft in the 
valley near the north line of sec. 12, T. 6 N., R. 23 E., or from one in 
the valley of Mountain Creek, in sec. (-, T. 6 N., R. 24 E., several square 
miles of coal can be brought to the hoisting- plant by gravity. 

The thickness and quality of these coals, however, throughout the 
lower part of the Cavanal Basin remain 
to be determined by the prospector. 

The area of each of the Witteville 
coal beds in the Cavanal syncline is 
nearly 60 square miles. 

/// the Scmsbois syncline. — The Witte- 
ville coals are not known to occur in 
the Sansbois syncline, although the 
strata in which they belong are present 
in the high slopes and on the top of 
Sansbois Mountain. As in Cavanal 
Mountain, the contact between the Sa- 
vanna and Boggy formations indicates 
approximately the horizon of the lower 
Witteville coal. It awaits the pros- 
pector to determine its presence, thick- 
ness, and quality. The crop of the 
horizon of these coals in Sansbois 
Mountain occurs chiefly in steep slopes 
and high divides in the dissected moun- 
tain, where the surface is generally 
talus covered. Should these coals oc- 
cur in the syncline, they would occupy 
a large area and for the most part 
would lie nearly horizontal. 

In the Potea/u and Sugarloaf synclmes. — In these synclines only 
small areas of the formation containing the Witteville coals remain in 
their crests. Should these coals occur here, they would not be easily 
accessible, and hence would not have great prospective value. 



Fig. 20. Section of the Witteville coals and 
associated locks at the Witteville mines. 



OTHER COALS IN THE EASTERN CHOCTAW COAL FIELD. 



A coal bed reported to lie of workable thickness occurs in the 
Bokoshe syncline nearly 3 miles east of Bokoshe. It has been pros- 
pected in the NE. ] sec. 34, T. 9 N., R. 2± E.. where the dip is low 
toward the southeast. A short distance, west of this prospect the 



296 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

strike changes to south, and then east, around the end of the trough. 
The width of the basin occupied by the coal will not exceed 2 miles. 
The survey of the area occupied by the coal is not complete, and 
further details can not now he given. 



MTNTNX - DEVE LOPMENT. 

Flic data for the following brief discussion concerning operations 
and output of coal were obtained from the annual reports of the United 
States mine inspector for Indian Territory, from officials of coal oom- 
panies, and from observations made during the field work. The sum- 
mary given in the appended table is not complete in all respects, chiefly 
because the history of operations and the output of coal of some 
abandoned mines could not be obtained. 

The mining development is discussed by mining districts, considered 
from west to east, which are naturally divided by conditions of geo- 
logic structure and by facilities for transportation. 

The development of the eastern part of the Choctaw coal field has 

been more recent than that of the western. This was caused by the 
location, in the first place, of the Missouri. Kansas and Texas Railway 
aero— the western part of the field in a 1 tout L872. Ten years later the 
St. Louis and San Francisco Railroad was built aCTOSS the eastern end 

of the field, but the mining interests of this company were chiefly in 
western Arkansas, and the de\ elopment of coal in the Indian Territory 
was neglected by this company. The Choctaw, Oklahoma and Gulf 
Railroad from Howe westward, running through the coal field gener- 
ally parallel with the crop of the coal beds, was built later and opened 
the western market. The coal in the eastern pari of the Choctaw Na- 
tion has had to compete with the Arkansas coals, which are generally 
of better grade and which have been mined extensively. Moreover, 
the locations of the mines in Indian Territory with respect to railroads 
are such that their development necessitates the building of branch 
roads. The Panama Wed. for instance, which will be an important 
source of merchantable coal, crosses the Kansas City, Pittsburg and 
Gulf and the St. Louis and San Francisco railroads nearly at right 
angle-. Any large development of this coal must therefore In 1 pie- 
ceded by railway construction connecting with the main lines. 

The coal of the Choctaw Nation improves in quality from west to 
east, and two additional beds are mined in the eastern part that are 
not known to lie productive in the western part. It may confidently 

be expected, therefore, that the eastern field will BUrpass the western 
in importance a- a coal producer. 



TAFF AND ADAMS.] DEVELOPMENT. 297 



MINING DISTRICTS. 

Gowen district. — Gowen is situated in the east end of the Hart- 
shorne Basin and is properly a part of the Hartshorne district. The 
name Gowen is here applied because it is the only mine in this district 
upon the map accompanying this report. The coal mined here is the 
Hartshorne coal, the same that is mined elsewhere in the Hartshorne 
Basin. 

Mine No. 3 of the Choctow, Oklahoma and Gulf Railroad Company 
is located at Gowen, in the eastern side of sec. 26, T. 5 N., 11. 27 E. 
It was prospected in 1880, but was not worked until 1899. It consists 
of a shaft 256 feet deep and a slope 3,200 feet distant on the north, 
which will eventually be connected with the shaft. The coal varies in 
thickness from 3 feet 6 inches to 5 feet and is clean of shale or other 
impurities. The dip at the slope is 5° S. The shaft is in the axis of 
the syneline, which pitches westward at a low inclination and with 
slight undulations. The main entry is carried westward along the 
axis of the basin, to which coal from the sides is collected on the main 
entry by gravity. The company has built a branch road from the 
main line east of Hartshorne to the mine and has erected a new and 
commodious hoisting plant at the shaft. 

Wilburton district. — The two Hartshorne coals occur at this place, 
separated by about 50 feet of sandstone and shale. 

The McAlester Coal and Mineral Company opened strip pits and a 
slope in 1895 at a point about 1£ miles west of Wilburton, at the east 
side of sec, 7, T. 5 N., R. 19 E. The coal here is about 4 feet thick, 
and dips 12° a little east of north. At this place operations were 
begun in 1899 by a new company, the Eastern Coal and Mining Com- 
pany. The McAlester Coal and Mineral Company operated mines in 
the western part of Wilburton, on the east side of sec. 8, T. 5 N. , R. 
lit E. At this place in 1897 two slopes were sunk, one on each coal 
bed, so that the coal could be operated by the same hoisting plant and 
discharged from the same tipple. The coal in the upper slope is 4 
feet <; inches thick, while that in the lower is 5 feet thick. The dip 
at these mines is 18° N. The output of the company since 1897 lias 
been principally from these mines. 

The Wilburton Coal and Mining Company opened slopes upon both 
the upper and lower Hartshorne coals in 1S97. The slopes are known 
as No. 1 and No. 2 and are located in the eastern part of sec. 10, T. ■"> 
N., R. 19 E. The upper bed is -1 feet 6 inches thick; the lower is 5 feet 
thick and is separated from the upper by about 50 feet of sandstone 
and shale. The dip is 25 N. Mine No. 3 is situated three-quarters of 
a mile west of Nos. 1 and 2 and is opened on the lower Hartshorne coal. 



298 GEOLOGY OF THE EASTEKTST CHOCTAW COAL FIELD. 

The bed here is u little over 3 feet thick. This company also has < >pened 
mines Nos. 4 and 5 upon the same coals in this vicinity. 

The Eastern Coal and Mining Company constructed a branch road 
in 1899 from the main line of the Choctaw, Oklahoma and Gulf Kail- 
road to a point about l£ miles west of Wilburton, where they reopened 
a slope previously operated by the McAlester Coal and Mineral Com- 
pany. They arc now sinking a shaft near this place and will connect 
with the old workings. 

The coal of both the upper and lower beds worked in this district is 
clean and of highly bituminous quality, as is indicated by the proximate 
analyses in the table on page 308. 

Old district.- Ola is a siding and small mining town on the ( Ihoctaw, 
Oklahoma and Gulf Railroad, '1 miles east of Wilburton. At this 
place the Ola Coal and Mining Company operates mines which are 
known as Slope-. Nos. L, 2, 3, and 4. No. 1 and No. 1 ; are separated by 

a distance of l. too feet. These slopes are located in sec. il,T. 5 N., 

R. 19 E., and are upon the lower Ilartshonic coal seam, which is aliout 
.". feet thick and dips N. 25 . Slope No. 2, which is east of No. 1. is 
upon the upper coal. Slope No. 4. opened in L899, is located on the 
wesl side of sec. 7. T. ."> N.. R. 20 E. The coal is from .~> feet to 5 feci 
4 inches thick, and is the lower llartshorne bed. The dip is 35 a little 
ue-t of north, kike the coal in the Wilburton district, it is clear 
of shale partings and is of good quality. 

Panola district. The mine at Panola is a slope upon a coal bed 
cropping 300 feet north of the station, near the east side of sec. 5, T. 
."> Y. R. 20 E. The mine was opened in L899 and is as yet hut little 
more than a prospect, the -lope being now only T"> feet in depth. 

This coal is stratigraphically in the horizon of the McAlester coal, 
and is so considered bj tl perators. The lied dips north, is 4 feet -2 

inches thick, and is divided in the lower part by L9 inches of shale. 

Redoak district. Two seams of coal were prospected at Redoak in 
1899. They are separated by from 60 to To feet of shale. These coal 

beds, which crop jusl south of the town, are in the S\Y. | sec 34, T. ti 
N.. R. -1\ E. They are aliout in the horizon of the McAlester coal, 
but it is not known that cither is it> exact representative. The beds 
are between 2 and •". feet thick, and have shale contacts both above 
and below. At present they appear to be clear of shalv impurities, 
and of good quality. The dip is nearly L0 N. 

Turkey Creek district. — The Turkey Creek Mining Company oper- 
ates ('. miles eas< of Redoak, near the line of the Choctaw. Oklahoma 
and Gulf Railroad. The companv began operations in L899 and opened 
two xains of coal, which arc probably the same as the two at Redoak. 
The mines are at the east side of sec. 'M. T. »'> X.. R. 22 E. The lower 
bed is 2 feet 4 inches thick and the upper one i> 2 feet L0 inches, and 



IAFF AND ADAMS.] MINING DISTRICTS. 299 

both occur in shale, as at Redoak. The lower bed has locally a hand of 
bony coal near the base. The dip of the coal here is nearly 20° N. 
The quality is reported to be good and is successfully exploited. This 
company also opened one of the Hartshorne beds 1 mile south of its 
mines and on the line near the quarter corner between sees. 3 and 4, 
T. -I \. . R. 22 E., and east of Turkey Creek. The coal in this pros- 
pect is nearly 4 feet thick and has a sandstone roof. The dip is about 
26 N. On the west side of Turkey Creek, in sec. 4, T. 5. N. , R. 22 E., 
another coal bed, nearly 4 feet thick, is prospected and is found to 
have a shale roof. This coal differs in character from the one on the 
east side of the creek. It contains local impurities and is termed 
''faulty " b}^ the prospectors. It is possible that the coal at the former 
prospect is the lower Hartshorne coal, while this is the upper, though 
the fact is not definitely established. 

Fanshawe district. — The same coal beds which have been prospected 
and mined in the Redoak and Turkey Creek districts have been opened 
at Fanshawe, on the south side of the railroad track, but have not been 
worked for market. The coal beds are in shale and dip north at about 
the same angle as the coal in the Turkey Creek mines. 

Pocahontas district. — The Hartshorne coal was formerly mined at 
Pocahontas, a station on the St. Louis and San Francisco Railroad, at 
which place both the upper and lower beds have a workable thickness. 

The Kansas and Texas Coal Company opened what was known as 
the Braidwood mine, near Pocahontas, in the SW. \ sec. 32, T. 6 N., 
R. 24 E., in 1890, and worked it for about two years. The mine 
remained idle from July, 1893, to December, 1894, when operations 
were resumed for about one year, and then the mine was abandoned. 
The upper Hartshorne bed at this place is 3 feet 4 inches thick. The 
lower Hartshorne bed is separated from the upper by about 50 feet of 
sandstone and shale, as at Wilburton, and is about 4 feet thick. The 
dip is 45° N. The coal is of good quality, but according to report the 
steep dip, together with the presence of abundant water and gas, pre- 
vented its being worked profitably. 

Two miles west of Pocahontas, at a place on the St. Louis and San 
Francisco Railroad formerly known as Bryan, a mine was opened in 
1889 and was operated by the Kansas and Texas Coal Company for 
about two years. It was located in the SW. \ sec. 36, T. 6 X., R, 23 E. 
The coal there is the same as at the Braidwood mine above described. 

The quality of the coal in these mines is reported to be of the usual 
good grade of the Hartshorne coal farther west in this held. 

Wister district. — The Cavanal coal has been prospected in the NW. j 
sec. 28, T. 6 N., R. 24 E., and in the NE. i sec. 27, T. 6 N., R. 24 E., 
3 miles and 2 miles west of Wister Station, respectively. The same 
coal was found in a well about one-half mile north of Wister. 



300 GEOLOGY OF THE EASTEKN CHOCTAW COAL FIELD. 

In the fall of 1899 a company began mining operations by slope on 
this coal at the prospect 3 miles west of Wister and 500 feet north of 
the railroad track, the success of which has not been learned. 

When examined the coal in the prospect had not been exposed below 
the level of the disintegrated rock, and its true thickness could not be 
determined. The coal as exposed, however, was :'. feet thick and 
dipped 18° N. 

Howe district. — The only mine in this district is at the mining camp 
of Potter, It miles southwest of Howe Station, in the east side of sec. 
3, T. 5 N., R. 25 E. 

The Mexican Gulf Coal and Transportation Company opened the 
mine in 1899. The coal is operated by a shaft L10 feet dee]) and by a 
slope from the crop of the coal in the ridge to the south. A new 
shaft. No. 2. -C>0 feet deep, was begun the same year in advance of the 
workings. 

Mitchell Basin district. In L899 Milby & Dow sunk a prospect 
slope on one of the Hartshome coal beds in the south side of this 
basin, in the southwest corner of sec. 88, T. 5 X.. R. 26 E. The coal 
is about 3 feet thick and dips 25 N. The high grade of the coal in 
this basin i- attested bj the analysis in the table on page 308, which 
was made from sample- collected at this slope. 

The Hartshome coals have been prospected throughout the Mitchell 
Basin by means of numerous bore holes by the Choctaw, Oklahoma 
and Gulf Railroad Company, and the whole area underlain by coal is 
held under Lease by this company. The Kansas City, Pittsburg and 
Gulf Railroad crosses the basin, giving ample facility for shipment, 
hut the company holding the leases has not -.ecu lit to develop the 
coal. 

Cavanal district. The coal which is mined three-quarters of a mile 
north of Cavanal Station, in the we>t aide of sec. IT. T. 6 N., R. 2~) 
E., is known as the Cavanal coal seam. The Kansas and Texas Coal 
Company opened a small mine upon this coal in L894. In 1897 it pro- 
duced about 500 ton.-. 

The Crescent Coal and Mining Company began work by reopening 
the old slope in L899. It has opened a new mine near by, parallel with 
the old slope, and constructed a branch road from the main line of the 
St. Louis and San Francisco Railroad, and has erected a new hoisting 
plant preparatory to shipping on an extensive scale. The coal at this 
place is •"> feet li inches thick, and .-hows a thin parting of shale. The 
dip in the slope is aboul 7 \ W. 

The quality is that of a highly bituminous coal, as its analysis, given 
in the table on page 308, would indicate. Roth its sulphur and ash. 
however, are higher than either the Hartshome or McAlester coals. 

Poteau district. — In the hill on the west side of Poteau Station a 



taii am, MINING DI8TSI0T8. 31 >1 

slope was opened on the Cavanal scam, but it has been abandoned. 
Why this coal was abandoned at this place lias not been explained. 
Presumably it was because a more profitable mine was opened in the 

Witteville coal in the vicinity. 

Witteville district. At Witteville two seams of coal have been 
opened. They are known as the upper and lower Witteville beds 
The upper Witteville is the coal which was called the Mayberry coal 
where it was formerly mined north of Cavanal Mountain. 

The Cavanal Coke and Railway Company opened the mine at Witte- 
ville in L894, and was reorganized in 1890 as the Indianola Coal and 
Railway Company. Their mine is a slope on the upper Witteville 
coal and is located in the eastern base of Cavanal Mountain, in sec. 15, 
T. 7 N., R. 25 E. The coal is 3 feet 10 inches thick and has a thin 
shale parting 1 inch to 2 inches thick near its center. The dip at the 
opening is 6 W., and at the face of the working in the mine is about 
3°. The lower Witteville coal has been prospected in the slope of 
the mountain below the upper Witteville coal, and is found to be 4 feet 
8 inches thick, and to contain two considerable shale partings. This 
coal company has constructed a branch road i'roui its mines to Poteau 
Station, a distance of 3 miles to the southeast. The coal from the mine 
is loaded by gravity in railway cars about 1,000 feet distant from the 
mine. 

The analysis in the table on page 308 indicates that this coal is nearly 
the same in quality as the Cavanal coal. Like the Cavanal coal. also, 
its structure is weak, but it is shipped successfully to market. 

Mayberry district. — The coal which is being operated at the mining 
town in the west side of sec. 11, T. 7 N., R. 24 E. is the same bed as 
the upper Witteville coal. 

The Choctaw Coal and Mining Company began operations in this 
mine in 1800. An extensive hoisting plant is being erected at the 
mine and a branch railway has been constructed to Shady Point, on the 
Kansas City, Pittsburg and Gulf Railroad. The coal at this mine is 
4 feet 6 inches thick, separated by shale into three benches, as follows: 
Coal, lower bench, i >k J inches; shale, 1 inch to 2 inches; coal. 12 inches 
to 14 inches; coal, upper bench, 16 inches. It dips nearly S. 

Jenson district. -Jenson is situated on the St. Louis and San Fran- 
cisco Railroad just over the State line in Arkansas, about 1 mile south 
of Backbone Ridge. Reference to il is made here in discussing the 
mining operations which are near by in the Choctaw Nation. The coal 
which lias been opened near this point is perhaps a continuation of the 
Hackett coal in Arkansas. In Indian Territory it is known as the 
Panama coal bed, from developments at the mining town of Panama, on 
the Kansas City. Pittsburg and Gulf Railroad, farther west. The Jen- 
son Coal Company opened a mine in L895 about 2 miles west of Jenson. 



302 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

south of the St. Louis and San Francisco Railroad, in sec. 9, T. 8 N., R. 27 
E. The coal is reported to have been faulted and lost, and the mine 
was therefore abandoned in 1807. The coal is 2 feet 10 inches thick 
and dips about 12 C SSE. 

The Kansas and Texas Coal Company has opened a mine known as 
the Doubleday mine, situated west of the St. Louis and San Francisco 
Railroad, about i miles from Jenson, in sec. 7, T. 8 N., R. 27 E. It 
was opened in 1895, but was not worked until 1899. The coal has been 
stripped extensively and is found to run unevenly. In the slope at the 
face there is 2 feet 4 inches of coal, above which is 7 inches of bony 
coal, and above this 2 feet 7 inches of coal. The company has erected 
a temporary hoisting plant and connected its mines to the main line of 
the St. Louis and San Francisco by a branch road. The operations are 
carried to considerable depths in order to determine the quality of the 
coal, and whether or not it may be faulted, before the erection of hoist- 
ing machinery and other appliances preparatory to general shipment. 

Three and a halt' miles northwest of Cameron the Panama coal seam 
has been opened by Mr. ('. <i. Adkins. The slope is located in see. 21, 
T. 8 N., R. 26 E. The scam i^- 1 feet thick, and is clean coal of splendid 
quality. It dips L5 a little easi of south. This coal is considered by 
the miners to be the same as one bench of the coal bed at the Double- 
day mine. At present this mine is worked in a small way. and the coal 
is hauled to Cameron for shipment. 

Panama district. The coal mined at this place is considered to be 
the same bed as that at the Adkins. Doubleday, and Jenson mines, and 
possibly the Kacketl bed in Arkansas. It is known as the Panama coal, 
its name being taken from the mining town of Panama, on the Kan- 
sas City, Pittsburg and Gulf Railroad. The Ozark Coal and Railway 
Company opened a slope mine in L899, situated in sec. 21, T. 8 N., R. 
25 E., one-half mile wot of Panama Station. The coal IS of high grade 
and is clear of shaly impurities. It i- :: feet In inches thick, and dips 
14° a little west of south. 

A branch load from the mine joins the Kansas City. Pittsburg and 
Gulf Railroad at Panama Station. The company has a new hoisting 
plant and is shipping coal actively. The coal at present goes chiefly 
to the Texas market. 

Pocola district. — The bed of coal in Arkansas north of Backbone 
Ridge, known as the Bonanza coal, is thought to continue westward 
into the Choctaw Nation, and is believed to be the same as that 
mined in the Pocola district. The Kansas and Texas Coal Company 
prospected the coal, and did some preliminary work about 1 mile 
east of Pocola in 1895. The coal is :; feet 11 inches thick, and dips 
10° N. One mile west of Pocola the same coal bed has been worked 
in a slope, chiefly for local uses. This coal dips about 15° N., is 3 



TAFF AMD ADAMS.] MINING DISTRICTS. 308 

feet 11 inches thick, and has a shale parting 3 inches thick near its 
center. 

Two small slopes were operated in this coal in the vicinity of Pocola 
by W. O. Hartshorne in 1895. The coal is reported to be 3 feet 10 
inches thick, and to dip 10° a little west of north. The total output 
as reported was 700 tons. 

There was some prospecting by the Fort Smith and Western Coal 
and Railway Company in 1890 at several places near Pocola, but only 
preliminary work was done. 



304 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 
Summary of mining operations. 





Location. 


i tampan; . 


Mine. 


Name of I oal 

horizon. 


Gowen 

Wilburton.. 

Da 


Sec.26,T.o N..R.17 E 

r.5 N...R.19 E 

Sec. I0.T.5 N.. R. 19 E 

Bec.7, i. 5 N.. It. 19 E 

19E. 

Bee. it. T.~. v. R.19 E 

■ V. R. 19 E 

Sec.7,T.6 N..R.20 E 


i hoctav . k 1 a- 

1 18 and Gulf 

Railroad Co. 
Mc Uesteri !oal and 
Mineral Co. 

Wilburton Coal and 
Mining I o 

Eastern i i 
Mining Co. 

Ola Coal and Min- 
ing Co. 

do 


No.8shaf1 .... 

Upper slope .. 
Lower Blope . . 
Slope No. 1.... 
SlopeNo.2.... 


Hartshorne 

Upper Hartshorne. 
Lower Hartshorne. 
Upper Hartshorne. 
Lower Hartshorne. 


Do 

Ola 


Slope No. i 


Hartshorne 

Lower Hartshorne. 

do 

i ppei Hai tsho] ae 
Lower Hartshorne. 


Slope No.l. 

Slope No.2 

Slope No 8. . 
Slope No, i ... 

Slope 


Pedoak 

I". 

Fanshawe... 
Pocahontas.. 


do 

do 


V.K.JI B 

- 

Sec. 82, T. 6 N..R.23 E 

S N . R.24 E 

1 B N..R.23 E 






Turkey Creek Coal 



Lnd Texas 

do 


- |i ipe No i .. 

Slope 

Braid wood 
mine. 

Bryan mine . . 


do 


do 

1 1 pper Hartshorne. 
[Lower Hartshorne 
1 1 ppei Hartshorne. 
[Lower Hartshorne. 

Cavanal (?) 

Bartshorai 

do 

i.o w er Harts- 
horne (?). 


Howe 


• N..R.26 E 

Sec. 17, T. 6 N.,B 2 

7 N..R.25 E 

Sei ii.i.7 N..R.24 E 

Sec. 9, T. 8 X..K.27 E 

Sec.7,T.8 N..R.27 E 

8ec.21,T.8N.,R.26 E 

Sec.21,T.8N.,R.25 E 


Gull Coal 

and 1 1 
tion <■>. 

MUbj & Dow 

Mlnin 
[ndianola Coal and 

Railway Co. 
Choctan ■ 

MinlDj 


Shaft No.l.... 
Shaft No.2.... 




<lo 

do 

<lo 


WiUevillr... 


Upper Witt 






Do 

Cameron — 
Panama 


Cansat and Texas 

Coal Co. 
C.G.Adkine 

( izurk Coal a o 'i 
Railway Co. 

uid Texas 


Iliill 111 eel a y 

slope. 

31ope 

do 

do 


do 

do 






do 










do 






w estern Railwaj 
Co. 







TAFF ANM ADAMS.] 



MINING DEVELOPMENT. 
Summary of mining operations. 



305 



Thickness 
of coal. 


When 
opened 


Output, in tuns, by years, fur years 
ending June 30— 


Total 

output. 


Remark -. 




1896. 


1S97. 


1898. 


1899 




Ft in. Ft. in. 

3 6 to •"■ 

■1 6 
5 

4 6 

5 


1899 

1897 

1897 
1897 










60.741 
48,062 

18,561 

1,008 
36, 880 


Tons. 

66, 741 

69,032 




[ 300 


3, 000 


3, .".00 
300 


10,170 


(This company's output in- 
I eludes that of a slope op- 
| erated by the Eastern Coal 
1 and Mining Co. since 1898. 


1 






4 

5 

5 

4 t; 

5 to 5 4 
4 2 


1895 

lv. 17 
1898 
1898 
1899 

1899 


1,008 Opened by the Wilburton 
Coal and Mining Co.; op- 
erated by the Eastern Coal 
and Mining Co. since 1898. 


| 




300 


8,740 


1 






















•_' 1(1 




























is prospected and proves to 
be 2 feet 4 inches thick. 

Prospected and mined for 
local uses. 

(Idle from July, 1893, to Dec, 


* 

3 4 

4 
3 


I 1890 

■ 1889 

1899 
1899 


























[ Output not reported. 

fAbandoned in 1892. output 
\ not reported. 














! 








6,258 


6, 273 








i 










3 

3 3 

4 


1899 
lxiio 
1804 
1899 
1895 
1899 
















Prospected by the Kansas 
and Texas Co. in 1894. 


7,989 


10,000 


23,866 


19,605 


6,000 


6,955 


2 10 

5 6 to 7 


3,800 


5,600 






9. 300 








Prospected in 1895. 


i 










3 10 1899 
:; u 1895 
























i'n ispect. 

Small workings; abandoned. 
Prospects, 


7oo 










700 





























21 QEOL, PT 2 20 



306 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 

COMPOSITION AM) ADAPTABILITY OF COAXS. 

Obviously the most satisfactory method of determining the adapt- 
ability of a coal is by means of a practical test with the exact condi- 
tions under which it is to be used. If, on the other hand, a given 
quality of coal must be used, then the conditions requisite to its 
economic utilization should be carefully studied. A proximate analy- 
sis, which determines the essential constituents, and a test of the 
physical properties, are. however, a fair index to the quality of a coal, 
and if rightly understood will determine to a considerable extent the 
use to which it is adapted. 

The principal uses to winch a coal is applied arc as a find in devel- 
oping heat, in producing coke, and as a source of illuminating gas. 
Of these the use a- a fuel is by far the largest. 

The constituent parts of a coal, as determined by proximate chemi- 
cal analysis, are: Water, lived carbon, volatile hydrocarbon, ash, sul- 
phur, phosphorus. 

Of these, the fixed carbon and volatile hydrocarbon may be consid- 
ered as tin' essential materials. The sulphur, phosphorus, water, and 
ash me in the nature of impurities. A portion of these may. however, 
be consumed in combustion. The fixed carbon and volatile hydrocar- 
bon are the fuel portions, and indicate the amount of heat which may 
be obtained in the combustion. The ratio of the fixed carbon to the 
volatile hydrocarbon has been called the fuel ratio, and has been taken 
as the basis for the classification of coals. It is perhaps die most 

satisfactory method, although there are certain distinctions which it 
does not express. It is based upon the assumption that the sulphur, 
phosphorus, water, and ash are accidental impurities, and are liable to 
vary from place to place and with the method of operating tin' mine, 
as well as from conditions affecting it after it has been taken from the 
ground. For example, the introduction of •"slate" or ••bony" coal will 
cause a variation in the amount of ash. while the fuel constituents 
remain in the same ratio to each other, although forming a smaller 
percentage of the coal. Two coals thus considered may be of the 
same quality but may differ a- to their impurities. 

Besides determining the value of a coal as a find the fixed carbon 
and volatile hydrocarbon are the essential constituents which deter- 
mine its value in its other uses; namely, in the production of coke and 
the manufacture of illuminating gas. Coke is a product of fixed car- 
bon and the illuminating gas a product of the volatile hydrocarbon. 
The coking or fusing of coal i-. however, not directly related to its 
composition, as would seem to be indicated by certain exceptions in 
which coals do not coke at all. the only safe ground for determining 
the coking quality being a practical test. In the manufacture of coke 
the impurities, notably the sulphur and phosphorus, are of vital 



tapf amd Adams.] COMPOSITION AND ADAPTABILITY OF COALS. 307 

importance since in the subsequent use of the coke in iron smelting the 
presence of sulphur and phosphorus are highly detrimental. Sulphur 

occurs in coal as iron pyrites (FeS„), as Sulphate of lime, or gypsum, 
which appears in thin white scales in the coal, and as free sulphur. In 
coking the sulphur is largely volatilized and driven off, but if it, is in 
the form of sulphate of lime it will remain in the coke. Methods of 
crushing and washing the coal are devised for separating the sulphur 
before it is converted into coke. The sulphur which is in the coke 
produces in iron which is smelted with it the undesirable quality of 
red-shortness- -that is, the condition of brittleness when hot. Coke 
should not contain over 1 per cent of sulphur as a maximum. 

All of the phosphorus in coal usually remains in the coke produced 
from it. Its influence upon iron is to produce the condition of cold- 
shortness — that is, brittleness in a cold condition. 

Ash is largely a negative element, with but little chemical influence, 
unless it is composed of siliceous matter, in which case it will produce 
clinkers, which are undesirable. The accumulation of the ash displaces 
the fuel and stops the draft, thus necessitating the frequent cleaning 
of the fire box. An excessive amount of ash is detrimental in the 
manufacture of coke and also in the use of the coke in the iron furnace, 
since it must be disposed of in the slag. 

ANALYSES OF COALS. 

The following table shows the composition of coals from the Eastern 
Choctaw coal field. The fixed carbon and volatile hydrocarbon are 
expressed in the right of the table as percentages of the total fuel 
constituents, and the fuel ratios are given as the index of the fuel 
qualities of the coal. 

The table of analyses of coals from the McAlester-Lehigh or West- 
ern Choctaw coal field is here repeated from the Nineteenth Annual 
Report of the Survey, Part III, page 456. It is inserted for the sake 
of comparison, and to this end the fuel ratios have been computed and 
added to the table. 



308 GEOLOGY OF THE EASTERN CHOCTAW COAL FIELD. 



^ « 



h i-i ?i 



3 3 



S 8 i 

it H o 



i c 



- 3 5 a 



« s 









c " r: *" : 






8 8 5 S S 
ri S S pi 8 



jz -- - 






: 



Si 



S S $ S S S 



- f- 3 : = 



ill 



1 IS 1 






a ! 



s ■ - 

IS 



S :f 



S?3£ 



TAKF AND ADAMS. 



ANALYSES OF COALS. 



309 



1 3 



3 1 

I I 

~s a, 

~ 8 



s 

a 

a 

a 


p'~ 


1.26 

1.47 
1 . 64 

1.49 
. 99 




s s s s s g 

£ 8 S § V? !j 


i£§d 


is a s 9 a s 

«? 5 § § s s 


c 

3 
O 




H 


: : b 

■ : 2 
: : .o 

1 i 1 

.2 • ? 

^ O ^ 

•a "°. £ 

j ; q 


Character of coke. 


i g c 

ill 

5 o > 
1 c . * 

22. 

g P. c 

hj p 


— 2 o : 
. | s | | 

' ■,- J! fl iff 9 ^>" 

~ 1 i.1 111 

►J J u 


§ = ,• 

AH - 

Pi ft 


.^ o o o o o 


31 


4- - • 


3 


| "= '-° a 


Sid 

S a o 


1 5 I I * * 


•onoBA ut ajn; 
-StOni 8S3[ 'j.ijjiuu 
aiqijsnqmoo aipu[OA 


■& 8 8 8 3 5 




sjnon 
K 01 QZ ^OS'H WAO 
onouA in aarnsiOK 


■85 S S S 8 S 

* " "' " "" * 







ill 

S g* u 
-" 1 g s 

o -<? ■§ = 
m H « 


1 * 

ill 

S g 

s a & 

CO CO 






1 

1 

a 

y, 


c 

: 
■9 o 

1 fl 
3 

W 


< 

1 


p 


s 

2 





5 S"? S § • £ r 5.2 

; j = i i i .: ; ; = 

■= = S s .5 I t -7 - -2 



2 fc S I 

° X .ox 

H - H CI 

a 

o 

J5 ™ 'S fl 

■s a-^m 



I -3 a I H 



: s 
S h 



H i - -2 =£ 



.2 5 2 



™ i „ .2 






S. 1 -S 

" - : - ? S ' " ^ 

5 o -^ t: x -2 — - - £ 



c - rt £ 



a I r 



?i M-a3«2jsgS 

| B ■« ^ ^ S a. ^ l .S 



5 a 3 ? 

IIS 

?5i 



_ 3 -s 5 g 

o P o - ° 



■§ -P = r a ; £ 5 « « 
llagl||2-Hl 

5*5 £|^g 112=5 

g g.E Cj = o ^ o J_ g 

H S S so 5 ° ^ t .S 3 

K f 1 § s 1 1 H I 



310 GEOLOGY OF THE EASTEKN CHOCTAW COAL FIELD. 

Methods of sampling. — As an aid to the proper appreciation of the 
valiu 1 of the proximate analyses of the coals recorded in the tabic, 
notes on the method of collecting samples arc submitted. The samples 
from the Panama (Ozark). Cavanal. and Upper Witteville (Mayberry) 
beds were taken from a number of railway cars, in each case loaded 
for shipment from the mines. The cars were carefully gone over 
and a great many specimens collected from both small and large 
pieces. These specimens were then broken, mixed, and again broken 
into small fragments. A part of the mixture thus prepared was taken 
for analysis. The samples from the Doubleday top vein, Doubleday 
lower vein, and the Mayberry mine were taken from the faces of the 
workings by first cleaning <>tl' the surface of the coal with a hammer 
and then making a section some »i inches in width from top to bottom 
of the vein. Theeoalthus taken was then broken into small pieces 
and thoroughly mixed and a sample was taken for analysis. The Lower 
Ilartshoine. Upper 1 Iartshcrne and llartshorne (Potter) specimens 
were taken at random from mine car- as they were brought from the 
mine to the tipple, until a large parcel was collected. These specimens 
were broken, mixed, and divided, and from a division the fragments 
were again broken ami samples taken for analysis. At the Potter mine, 
where the slope had been driven down about ion feet, and where several 
carloads were upon the dump, very many specimens were collected at 
random, so that an average collection was taken. This collection was 
then broken and divided and samples for analysis were taken as indi- 
cated above All of these sample- were shipped from the field to the 
office in heavy canvas bags, so it will be observed that the moisture rep- 
resented in the tabic of analysis is probably a minimum for these coals. 

CLASSIFICATION OF COALS. 

According to the variation of their fuel ratios, coals have been 
classed a- exhibited in the following tattle: 

Hard, dry anthracite, ratios varying from LOO to \- 

Semianthracite, ratios varying from 12 to 8 

Semibituminous, rati"- varying from s t<> 5 

Bituminous, ratios varying from 5 to <i 

In this table it will be seen that theoretically the ratios vary from 
zero to loo. while practically they do not exhibit so wide a range. 
The classification was made for black or stone coals, and consequently 
the brown coals or lignites would not be included. In the trade the 
classes are not strictly observed, but they afford as satisfactory a basis 

as has yet been proposed. 

Considered according to this classification the coals of the Eastern 
Choctaw coal field are bituminous, having ratios varying between 1.83 
and 4. ?."». with the exception of the coal from the Panama seam at the 
Ozark mine, which, according to the analysis, has a find ratio of :>.:;:_'. 
which places ir just within the limit of the semibituminous class. 



VARIATION OF COALS. 311 



VARIATION OF COALS. 



The coals which are at present mined in a commercial way in the 
Eastern ( Jhoctaw coal field, are found in three horizons. Their geologic 
occurrence has a wide range, and a variation in the quality of the coal 

beds may be naturally expected. Only one of the beds, the Ilarts- 
horne or Panama, has sufficient geographic range to indicate variation 
throughout the extent of the held. 

Comparing the fuel ratios of the various seams of coal in the region 
where all of them are closely associated, so as to exclude, as far as 
possible, variation with their geographic extent, we find that the coal 
of the Hartshorne seam at Howe has a fuel ratio of 3.20, and at 
Heavener, 3.23. Its equivalent, the Panama seam at the Ozark mine, 
shows a ratio of 5.22. The Cavanal seam at Cavanal has a ratio of 
2.81. The fmd ratio of the coal from the upper Witteville seam is 
2.7s, and at the Maberry mine it is the same. This comparison points 
to the fact that the lower coals have a higher fuel value. 

The fuel ratios of the coal from the Hartshorne and Panama scams 
are seen to he higher in the eastern part of the field. At vVilberton 
the lower seam lias a find ratio of 1.40 and the upper a ratio of 1.33. 
At Howe and Heavener the ratios are 3.29 and 3.23, respectively. 
The ratio of the lower coal at the Doubleday mine is 1.57 and that 
of the upper 4.73, while the coal from the Ozark mine at Panama 
has a fuel ratio of 5.22. 



PRELIMINARY REPORT ON THE CAMDEN COAL FIELD 
OF SOUTHWESTERN ARKANSAS 



JOSEPH A. TAPF 



C N T E N T S 



Introduction 319 

Location of the coal field 319 

Character of the country 319 

Age of the coal-hearing rocks 320 

Character of the rocks 32] 

Occurrence and structure of the coal 322 

Mining development and details of coal sect inns 323 

Composition of the Camden coal 325 

Physical properties 325 

Chemical composition 325 

Table of proximate analyses 32ti 

Proximate analyses of air-drieil < !amden coal 327 

Technical analysis 328 

Gas-producing qualities of Camden and other coals 329 

315 



I LLU ST RATIONS 



Page. 
Plate XXXVIII. Map of part of southern Arkansas, showing the area of the 

Camden coal field examined 320 

XXXIX. Map of the Camden coal field, showing crop of coal and 

location of mines and prospects '. . 322 

317 



PRELIMINARY REPORT ON THE CAMDEN COAL 
FIELD OF SOUTHWESTERN ARKANSAS. 



Bv Joseph A. Taff. 



INTRODUCTION. 

The following report is based chiefly upon field work done in May, 
1900, although the writer was already somewhat familiar with the 
region and its geologv. The specific object of the report is to describe 
the mode of occurrence, extent, and economic value of the coal in the 
vicinity of Camden, on the Ouachita River, Ouachita County, Arkansas. 
In connection with the examination and mapping of the coal the geol- 
ogy of the associated rocks was investigated as far as possible. 

The country has low relief and is densely forested, while the rocks 
arc soft and almost completely covered by soil, so that it would be 
difficult to make a satisfactory report on the geology of the region, 
even after a complete survey. 

LOCATION OF THE COAL FIELD. 

The part of this coal field examined by the writer lies in the north- 
central portion of Ouachita County, Arkansas, contiguous to the 
immediate valley of Ouachita River, and to the Camden branch of the 
St. Louis, Iron Mountain and Southern Railway. It includes nearly 
50 square miles, as shown on the sketch map (PI. XXXVIII). The 
larger part of this area is in T. 12 S. , R. 18 W. , where most of the active 
prospecting and mining has been done. The coal-bearing rocks are 
exposed east, west, and south from the district examined. Through- 
out a broad area, which covers parts of several counties, the same 
coal is reported to occur, but, chiefly on account of facilities for trans- 
portation, the Camden held has been more extensively prospected and 
developed than any other locality in southwestern Arkansas. 

CHARACTER OF THE COUNTRY. 

The surface of this portion of Arkansas consists of broad alluvial 
river valleys and a dissected upland. The valleys consist of first and 
second bottoms bordering the rivers and larger creeks. Their surfaces 

319 



320 THE CAMDEN COAL FIELD OF AKKANSAS. 

are covered by sands and silts deposited by the streams during floods. 
At present the high waters of these streams cover only a part of the 
alluvial valley lands, the first bottoms. 

The extent of the alluvial lands as represented on the map (PI. 
XXXYIII) is adopted from the Annual Report of the Arkansas Geo- 
logical Survey for 1888, Volume II. So far as the writer's examina- 
tion extended, the outlines there given air substantially correct. 

At the border of the alluvial bottom lands the surface rises rather 
abruptly, nearly 150 feet, to the general level of the highland. The 
rocks in the highland are of such a nature that they disintegrate 
readily, permitting the small streams to cut their way rapidly down- 
ward. As a result the surface of the highland, especially near the 
river, is dissected by a very irregular system of drainage channels. 
Even the rivulets, l>\ headwater erosion, have cut small gulches in the 
soft rock, often to their sources. 

V(.l. OF THE COAIi-BEARHSTG ROCKS. 

In 1859-60 Dr. If If Owen made a reconnaissance of the southern 
counties of Arkansas, during which he examined the geology of 
Ouachita County. In his report 1 lie give- tin' results of his exami- 
nation of the coal which occurs in sec. L2, T. 12 S.. R. L8 W., and 
\\ hich he calls "the ( 'amden coal." 

In the Annual Report of the Geological Survey of Arkansas for 
fs.s.s. Volume 11. pages 50 51, Mr. R. T. Hill discusses the geology 
of the rock- iii the region we-t of ( 'amden and north of Texarkana. 
.Mr. Hill determined that the rock- of the ('amden coal held belong to 
tlie epoch of the Eocene Tertiary, and calls the coal-hearing formation 
the Camden series or Camden formation. He states that it extends 
from Louisiana across southern Arkansas into Texas. He reports the 
occurrence of lignites or ligneous shales in the bluff of Ouachita River, 
near Camden, and at the mouth of Little Missouri River. Mr. Hill's 
work was confined to the valley of Ouachita River in his surveys in 
Ouachita County, and hence he did not Bee the Camden coal. 

Mr. Gilbert If llarri- published a report on the rocks of Ouachita 
County in his volume of tin • reports of the Arkansas Geological Survey. 2 
It was Mr. Harris's object first to determine the age of the rocks by 
means of the fossil shells which they contain, and then to describe 
their character. He investigated many localities in Ouachita County, 
as well as those on the Ouachita River visited by Messrs. Owen and 
Hill. Mr. Harris visited the mine in sec. 12, T. 12 S., R. 18 W., and 
reported Owen's section of the coal to he substantially correct. 

Mr. Harris verified Mr. Hill's determination of the Eocene age of 
the coal-hearing rocks of ( >uachita ( lounty and classified them with the 



id Dale i mm. Vol. II. I860, pp 
-'Ann. Repl Vol. II. 1892, pi 



U. S GEOLOGICAL SURVEY 



TWENTY-FIRST ANNUAL REPORT PART II PL. XXXVIII 




MAP OF A PART OF SOUTHERN ARKANSAS 

SHOWING THE AREA OF THE CAMDEN COAL FIELD EXAMINED 

By J. A. Tall 
Scale of miles 



1899 



•iui.1 CHARACTER OK THE ROCKS. 321 

Lignitic stage of Mississippi and Alabama. He reports that these coal- 
bearing rocks form the surface of considerable areas in 1 )allas, ( hiachita, 
Columbia, Hempstead, Lafayette, and Miller counties, Arkansas. 

CHARACTER OF THE ROCKS. 

The rocks in the part of the Camden coal Meld examined by the writer 
are soft sand and clay shales, except local ferruginous sandstone and 
ironstone segregations. These sands and clays are compact, but not 
consolidated. The fresh clays are plastic when wet, and the sands, 
except where locally indurated, are friable and break down soon after 
exposure. As a result of these characteristics fresh exposures of rock 
are exceedingly rare. Occasional cuttings in old roadwa} r s, recent 
excavations at mines, and exposures at some of the numerous springs 
which issue from the coal outcrop give the only fresh rock exposures. 

The following generalized section has been constructed from numer- 
ous separate outcrops, from exposures at coal openings, and from the 
character of soil and partially decomposed rock over the highland. 
Although far from satisfactory, it is the best that can now be made. 

Generalized section of rocks occurring in the Camden coal field, Arkansas. 

Feet. 

1. Sand and sandy clays, weathering yellow and red, with local hard beds 

of ferruginous sandstone and low-grade siliceous iron ore, from the 

top of the section downward 50 to 60 

The sand is more abundant than the clay in these beds, which are best 
seen in the hilly country along the road between Lester and Camden. 
The ferruginous sandstones occur in thin, hard plates, and as beds 
and segregations a foot and lens in thickness. 

2. Thin interstratified beds of sand, sandy clay, and clay, yellow to light 

blue in color 40 to 50 

In these strata the sand becomes generally less abundant downward, 
and at the base there is a bed of clay 4 to 8 feet thick resting upon 
the coal. This clay above the coal is light blue or ash colored, 
homogeneous and plastic when wet. 

3. Coal 2to 3.5 

Reported to be in places <> feet. 

4. Light-gray or bluish clays, not well exposed, reported to be 10 to 20 

The clays associated with the coal are partially exposed at the mines 

in sees. HI, li', 14, and 25, T. 12 S., R. IS W.; in sees. 11 and 12, 
T. 13 S., U. IS \V., and in sees. 7 and 19, T. 12 8., R, 17 W. 

5. From the clay beneath the coal down to the level of Ouachita River 

hott the rocks are < cealed through an interval of to 30 

The rocks are well exposed in the bluffs at the mouth of the Little 
Missouri, where the river is cutting into the highland, a few miles 
north of the outcrop of the Camden coal. They are also exposed at 
Camden, where the river again approaches the highland. The latter 
locality is south of all the known occurrences of coal in this held. 
2d oicol, PT 2 21 



322 THE CAMDEN COAL FIELD OF ARKANSAS. 

Having been taken at the only good exposures of the rocks in this 
region, the sections as given by Mr. Hill 1 are reproduced below. 

Section at mouth of Little Missouri River, Arkansas. 

Feet. 

1. River alluvium 20 

2. Ferruginous conglomerate ( Quaternary) ,. 6 

:;. Thin band of lignitic sand, same character as No. :'> of the Camden section. 

4. Micaceous line sand 1 

5. Alternating lignitic and sandy strata to water level " 8 

Section of bluff of Ouachita River near Camden, Arkansas. 

Feet. 

1. Sandy soil 5 

2. Laminated sand with greensand specks, originally white, weathering red . . 152 

:;. Lignitic shales interstratified with white sand 20 

l. Buff-colored micaceous sand and clay, weathering pink and light yellow. . 10 

5. Bituminous shales with concretions of iron pyrites, weathering reddish col- 

ored 15 

6. Fine micaceous sand and clay, laminated 25 

7. Concealed strata 25 

S. Fine sand and clay similar to Xo. (i. to water line 10 

The Camden coal, withoul doubt, belongs above the section at the 
mouth of kittle Missouri River, since its northernmost outcrop now 
known occurs 4 miles farther south and at a higher elevation above 
the river than the top of Mr. Hill's section. The outcrop of coal 
Dearest the Camden section is thai at the lb-own mine, 5 miles north- 
west of Camden. The coal bed can not be traced from this mine to 
Camden by means of surface outcrops, and hence its position in the 
section given above has not been accurately determined. 

OCCURRENCE \M> STRUCTURE OF THE COAL. 

The approximate location of the outcrop of the Camden coal bed is 
shown on the map (PI. XXXIX) as it occurs on the easl side of the 
field between the neighborhood of Camden and French Creek. 

The Camden coal extends into the highland westward from Ecore 
Fabre (feck, and i^ reported to crop out in the valleys at a number 
of places through western Ouachita County. 

Whether <>r not these isolated outcrops west of the area surveyed 
tire upon the Camden coal was not determined. They are reported 
by a prospector to he the same in character as the Camden coal and to 
occur in the same stratigraphic position. 

The Camden coal bed and the rocks associated with it when exam- 
ined locally appear to lie in. a nearly horizontal position. When con- 
sidered over ti large area, however, the rocks are found to dip or 
incline southward, approximately the 9ame as the fall of the Ouachita 

'Aim. Rept. Geol. Survey Arkansas, Vol. II. 1888, p. 50. 



U. S GEOLOGICAL SURVEY 



TWENTY-FIRST ANNUAL REPORT PART II PL XXXIX 




EN ttCO. LITH I 



MAP OF PART OF THE CAMDEN COAL FIELD 

SHOWING CROP OF COAL AND LOCATION OF MINES AND PROSPECTS 
BYJ.A.TAFF 
Scale of mil' 



1899 



taff.] OCCURRENCES AND STRUCTURE OF THE COAL. 323 

River. At the north end of the Held, in sec. 25, T. 1 1 S.. R. 18 W.,at 
the mines in T. 12 S., R. 17 W., and at the Brown mine, in sec. L2, 
T. 12 S., R. 18 W., the coal outcrops at nearly the same distance ahove 
the overflow' limit of Ouachita River. Slight undulations or " rolls" 
occur in the beds, which have no apparent system or regularity of 
bearing. In places the floor rises and falls without corresponding 
undulations in the roof, and thus causes local thinning and thickening 
of the coal. 

Minimi <lt rdojnin at <iu<l details of <-<><d sections. — The Brown mines 
are on the east side of sec. L2, T. 13 S., R. 18 W. The coal in the 
vicinity of these mines crops in the slopes of hills facing Ouachita 
River bottom, about -10 feet above the overflow line. The coal is being 
mined in a small way by two drifts which have been driven in about 
50 feet. From the entrance of the east drift inward about 40 feet the 
coal is practically horizontal. Near the face, however, the floor of 
the coal rises toward the south, causing the coal to change in thickness 
from about 3| feet to little less than 3 feet, with clay above and below. 

Near the center of the north side of sec. 11, T. 13 S., R. 18 W., a 
drift, known as the Williams mine, has been opened at the head of a 
small branch of Ecore Fabre Creek. The mine was closed, and when 
visited the door was locked, so that an inspection of the coal at the 
face of the workings could not be made. It is reported by citizens 
living in the neighborhood, however, that the coal is about 3£ feet 
thick and occurs in the same manner and is of the same quality as that 
in the Brown mines. Light-blue and whitish clays several feet thick 
are exposed above the disintegrated coal at the opening of the mine. 

In the NE. \ of SW. \ sec. 25, T. 12 S., R. 18 W., Mr. Joseph 
Dempsey has cut a drift on the coal for about 40 feet. The coal is 3 
feet thick, is horizontal, and has a clay roof and floor. In order to 
give the mine proper drainage the drift was cut in the lower part of 
the coal and in clays below, so that the full thickness of the coal is 
not yet exposed. 

Near the center of sec. 14, T. 12 S., R. 18 W.,two drifts were 
opened several years ago upon the coal for a distance of 60 feet 
toward the northeast. The company operating the coal built a branch 
road nearly 3 miles long from the Camden branch of the St. Louis, 
Iron Mountain and Southern Railway to the mine. It is reported that 
on account of insufficient timbering and the presence of water the day 
roof gave way and blocked the mine entry and the mine was aban- 
doned. The coal in these mines is said to range from 5 to 6 feet in 
thickness. 

The mine in the NE. ±. sec. 12. T. L2 S.. K. is W., is the oldest 
known in this district. The coal at this place was examined and 
reported upon by Dr. I). 1). Owen. State geologist of Arkansas, in 



324 THE CAMDEN COAL FIELD OF ARKANSAS. 

IStiO. 1 Dr. Owen reported 6 feet of coal in the old mine, which is 
now closed. A new drift was recently opened beside the old mine to 
a distance of 50 feet, and the coal at the face of the new mine is 3 feet 
6 inches thick. This coal was also examined by Mr. G. D. Harris, of 
the recent Geological Survey of Arkansas, about 1892. Mr. Harris 
reports the same thickness of coal as is given by Dr. Owen. The dis- 
crepancies between the observations upon the coal section by Messrs. 
Owen and Harris and by the writer may be explained by the prob- 
ability that the coal varies in thickness within short distances, caused 
by the undulations of the clays in the roof or floor of the coal, as 
above referred i<» in the lb-own mine. At the time the writer visited 
this mine the clays both above and below the coal were not exposed to 
the extent reported by Dr. Owen and Mr. Harris. 

The mines in sees. 7 and L9, T. L2 S. , li. 17 W..were opened a num- 
ber of years ago and were worked at intervals for some time, but are 
now abandoned. The coal occurs al practically the same level as that 
in sec. L2, T. L2S.,R. L 8 W. , and is reported by the operator to be of 
about the same thickness and of the same general character. Bluish 
clays occur at these mines in contact with the coal, as at other mines 
in this region. 

An opening on coal in sec. 2, T. L3 S., K. 18 W.,and on the branch 
road extending southwestward from the lumber mills at Lester Station, 
is known as the " Brati prospect." The shaft was sunk about 40 (Vet 
and a small quantity of coal was taken out. When visited the shaft was 
partially tilled with water and the coal could not be examined. It is 
reported by the owner to be about :! feet thick. Bluish clays were 
upon the dump and are reported to come from both above and below 
the coal. 

The outcrops indicated on the map (PI. XXXVIII) are all natural 
exposures of the coal occurring at Bprings which issue from the sandy 
strata above the clay bed overlying the coal. On account of the dis- 
integration of the rocks a full section of the coals could not lie obtained 
at any of these outcrops. The clays are exposed either above or below 
the coal, and in nearly all of these outcrops the nature of the clays as 
well a-- of the coal is found to vary but little from that reported as 
occurring at the mine- and prospects. 

The prospects indicated on the map in the western side of T. 13 S., 
K. 18 W.,are provisionally located from information giveD by a pros- 
pector who has worked extensively throughout this part of the Camden 
coal field. 

From the sections of the coal bed observed and reported on good 
authority it may be safely concluded that it extends continuously 
throughout the district examined, except where removed by erosion, 



taff.] COMPOSITION OF THE COAL. 325 

and that its thickness is at Least 3 feet, ranging from that to 6 feet. It 
is estimated that the single township (T. 12 S., R. 18 W.) in which the 
bed h;is been most thoroughly prospected contains over 75,000,000 ton's 
of coal. Of course not all of this can be mined; but even if only half 
of it is available, the held is capable of sustaining a large output for 
many years. 

COMPOSITION OF THE CAMDEN COAL. 

It is necessary to discuss the composition here only so far as it bears 
on the adaptability of the coal as fuel and for the production of illu- 
minating gas and oil. To this end its physical properties will be con 
sidered first, and then its chemical composition. 

Physical properties. — The physical properties which have an impor- 
tant bearing- upon the use of the coal as a fuel are its color, texture, 
fracture, hardness, and its power to give out and absorb water under 
different conditions of exposure. 

The Camden coal as it comes from the mine is brownish black and 
compact and has a generally uniform, even texture or structure. 
Occasional fragments of lignite with clearly marked woody structure 
may be seen. It has an uneven, conchoidal fracture. It is soft but not 
friable; that is, it may be easily mined with a pick and maybe cut with 
a knife as readily as compact dry clay, but it will not crumble between 
the fingers. When cut or scratched with a knife it shows a shiny or 
oily streak. Upon being exposed to dry air the coal contracts and 
cracks, both along the bedding and at right angles to it, so that frag- 
ments may be broken by the hand, but the mass does not fall to pieces. 
The coal is then blacker and harder than when fresh, and the streak 
or powder is more nearly black. On being exposed for a short time 
to the repeated action of rain or dew and sun, however, it will disin- 
tegrate into small particles. The cracks along the bedding plane 
bring out the lignitic or woody structure and at the same time make 
plainer the stratified character of the coal. 

The percentage of water contained in the coal as it comes from the 
mine is expressed in the first column of figures in the table of analyses. 
The percentage of water in the coal after it is dried in air, the loss in 
such drying, and the amount of water which the dry coal will absorb in 
moist air are given in the last three columns of the table, respectively. 
The water lost in dry air is technically called "hygroscopic water," 
and it is the loss of this water which causes the coal to shrink and dis- 
integrate on exposure to dry air. Its power to reabsorb and to liberate 
this hygroscopic water on repeated wetting and drying is the cause of 
its rapid and complete disintegration when exposed to the weather. 

Chemical composition.- — A proximate chemical analysis of a coal is 
that usually made for determining its commercial value. Such an 



326" 



THE CAMDEN COAL FIELD OF ARKANSAS. 



analysis expresses very nearly the amounts of the various products 
of the coal which determine its uses and value. These products are: 
(1) Water, (2) volatile combustible matter, (3) fixed carbon, (4) ash. and 
(5) sulphur. Of these five substances only the volatile combustible 
matter and fixed carbon are essential. They form the fuel of the coal, 
while the other substances are waste. The value of the coal as a fuel 
depends chiefly upon the percentage of fixed carbon, it being more 
stable and producing more heat upon oxidation than the volatile com- 
bustible matter. The latter includes the combustible gas, oils, and 
tar of the coal, and is easily kindled and rapidly consumed. 

Coals are classified according to the ratio of their fixed carbon to 
their volatile combustible matter. When this ratio is more than 1 and 
less than .3 — that is, when the percentage of fixed carbon is greater than 
that of the volatile combustible matter, but less than five times as great — 
and when the water is less than In per cent, the coal is classed as bitu- 
minous. When the above ratio is less than 1 and the percentage of 
water more than Id. the coal is classed as lignite. The greater the 
ratios between these two products the higher is the grade of the coal. 

Instead erf aiding combustion the water consumes heat in being 
evaporated from the coal when the latter is burned. Water, there- 
fore, has a negative value and is an important (dement in the classifi- 
cation of coals. When the content of water ranges above 10 per cent 
the coal is usually classed as a hrown coal, or lignite. 

The sulphur in coals usually occurs in combination with iron, and by 
its oxidation it aids combustion slightly, but it attacks and corrodes 
the grate bars and boilers. It is therefore decidedly objectionable, 
and coals which contain large percentages of it become practically 
valueless as fuel. 

'/'.>/,/, of proximate analyses. 





Variety pfcoal 


LocaHt, 


Water 
in 

fresh 

coal. 


Vol.. 
tile 

Im'v't'i- 
1,1.- 

mat- 
ter. 


Fixed 

ear- 
lion. 


\-l, 




Water- 


,. 


Sul- 
phur. 


Re- 
tained 

in dry 
air. 


Lost 
in dry 
air. 


Reab 
sorbed 

in 
moist 
air. 








/'. , ct. 


Percl 


Vircl. 


Peret. 


Perct. 


Perct. 


Perct. 


l'rr el. 


1 


Brew n & ii 


Brown mine.Ouach- 


38.72 


86. 90 


16.90 


7.50 


0.50 


11.23 


27.49 


/ill. is 




lignite, n 


ita County, A r- 






















, kansas. 














- 


Brown coal, or 
lignite. 


See.l2,T.13S.,R.18 
\\\, Ouachita 


> -in .: 11 


19.95 


:,. 85 


.42 11.08 


■211. 06 


Ml. is 






j County, Arkansas. 










3 


Brown coal, or 
lignite. 


See. 10, T. 12 S., R. 18 32. 76 

\\\, Ouachita 


23. 32 


1 1 . 32 


18 9.81 28.09 


610.25 






County, Arkansas. 









(Analyses l-:; made in the laborato: 

In 154 hours. 



ie United stales ecological survey, bj George Steiger. 



COMPOSITION OK THE COAL 



327 



Table i) f J mi i i mi iir analyse* — ( lontinuei 
ANALYSES FOB COMPARISON. 





Variety of coal. 






Vola- 
tile 
com- 
busti- 
ble 
mat- 
ter. 


Fixed 
bon. 


Ash. 


Sul- 
phur. 


Wat. r- 


No. 


Locality. 


Water 

in 
fresh 

coal. 


Re- 
taincd 
ill drv 

air.' 


L. .St 

in dry- 
air. 


Reab- 
sorbed 

in 

moist 
air. 


4 
5 


Brown coal, or 

lignite./) 
Brown coal, or 
lignite.') 


Wood county, 
Texas. 

Mi lam Coun ty, 
Texas. 

Nacogdoches 
County, Texas. 

District of Alberta, 
northwest Canada. 

Lewis River, north- 
west Canada. 

Mill Creek district, 
Alberta, north- 
west Canada. 

Huntington, Sebas- 
tian County, Ar- 
kansas. 


Pint. 
10. 85 

16.40 

L6.82 

11.68 

6.03 

1.63 

[ .92 


Per ct. 
37.82 

41.52 

46. 32 
35. 82 
36.92 
28. 43 

15. 54 


Perct. 

38.21 

31.47 

49.88 
49.03 

57. 38 

77. 53 


Perct. 
12.35 

7.70 

5.37 

2.62 

8.02 

12.37 

4.84 


Perct. 

.77 

.96 
1.09 

1.14 


Perct. 
6.15 

S, TO 

7.15 
4.19 
2.81 
. 38 

1 Not 
l det. 


Perct. 

4.70 

7.70 

7. 49 
3. 22 

Not 
det. 


Perct. 
al0.25 

al0.25 


7 
8 


Lignite <• 

Lignitic coalc .. 


12. 09 

8.80 


10 


Bituminous 
coal, d 


Not 
det. 



n In 154 hours. 

6 Geological Survey of Texas, 1892: Brown coal and lignite. 

■ i in hygroseopicity of certain Canadian fossil fuels: Trans. Royal Soc. of ('ana 

(I Arkansas Geological Survey, Vol. II, 1888. 

I'roriiinili iiiiu/i/ms nf uir-il ri< il ( 'nmili'ii mill. 





Water. 


Volatile 
combus- 
tible 
matter. 


Fixed 
carbon. 


Ash. 


Sulphur. 




Per cent. 

11.23 
11.03 
9.81 


/'. r r, ul , 

44.04 
17. 91 
Id. 29 


/v r r, ul 
33.69 
32.81 
29. I:: 


Per cent. 

11.04 
8.25 
14.47 


I'n- nut. 















The samples 1, 2, and 3 of the Camden coal were collected from the 
fresh faces of the mines, and represent complete sections of the bed. 
They were transported to the laboratory in air-tight vessels to avoid 
loss of moisture The first table gives the percentages of the various 
constituents of the coal as taken from the mine and containing all of 
its original moisture, the second table the percentages of the constit- 
uents after exposure to dry air for some time. The last represents 
the composition of the coal as it reaches the market. 

In the hygroscopic tests of these coals a unit weight was finely 
divided and exposed to dry air until it reached a constant weight. 
This gave loss of water shown in the table under per cent of water 
"lost in dry air." The percentages of water gained in moist air are 
the results obtained by exposing the same coal for 154 hours to air 



328 THE CAMDEN COAL FIELD OF ARKANSAS. 

saturated with water. At the end of this time the coal was absorbing 
water at the rate of 0.2 per cent in 24 hours. 

The brownish color of the Camden coal, its conchoidal fracture, its 
pronounced woody structure in part, and its loss of water and dis- 
integration on drying are the physical propei'ties which class it with 
brown coal or lignite. 

The chemical analyses Nos. 1, 2, and 3 in the first table represent 
the composition of the coal as it comes from the mine. They show 
that it contains an unusually high percentage of water and a relatively 
low percentage of fixed carbon. The amount of sulphur is unusually 
low. which is in its favor. The percentage of volatile combustible 
mutter is that usually found in the highly bituminous coals. 

The low fuel ratio, less than 1 in both the fresh and air-dried sam- 
ples, and the high percentage of water place this coal below the bitu- 
minous grade, and in that of brown coal or lignite. The composition 
of the air-dried samples corresponds with that of fair-grade brown 
coals or lignites found in rocks of the same age in Texas and Canada, 
as shown in the analyses given for comparison in the first table. 

From the chemical analyses it is concluded that the Camden coal 
fresh from the mine would probably not prove successful as a find on 
account of the large quantity of water which it contains. It is believed, 
however, especially on account of the low percentage of sulphur, that 
the air-dried coal, if used on specially constructed grates with properly 
regulated draft, would make a good domestic and steaming fuel. 

Technical anribysis.- In orderto ascertain the gas-producing qualities 
of the Camden coal a quantity of it was shipped to the Pittsburg Test- 
ing Laboratory. Limited, of Pittsburg. Pennsylvania, for testing. 
The test was made under the following conditions: 

The apparatus consisted of a cast-iron retort set horizontally in 
brickwork, heated by natural gas. Connected with the retort was a 
system of iron tubes which were cooled by contact with the air. In 
these the tar and water condensed. The gas then passed through about 
4 inches of water in a rectangular copper vessel, called the scrubber, 
and thence to a cylindrical purifier, containing dry slaked lime. It 
next passed through a gas meter, and was finally collected in a cylin- 
drical holder. 

For photometric work a standard sperm candle in a Bunsen photom- 
eter was used. The gas was burned at the rate of 5 cubic feet per 
hour in an Argand burner. Ten readings were taken and the results 
were averaged. By the use of tables the volume of gas obtained was 
calculated to standard temperature and pressure. The temperature 
of the retort was between 1,800° and 2,000° F. 

The test was made under the direction of a man familiar with 
practical gas manufacture. 



GAS-PRODUCING QUALITY OF THE COAL. 



329 



The quantity of gas obtained per ton of 2,000 pounds of coal was 
11,386 cubic feet of 22.3 candlepower. 

The following table enables a comparison to be made between the 
Camden coal and other standard gas coals. The first six coals in the 
table were tested by the same apparatus under similar conditions and 
the results are. therefore, strictly comparable. 

Gas-producing qualities of Camden and other coals. 



No. 


Character of coal. 


Source of coal. 


Cubic feet of gas 
per ton of coal. 


Candle- 

powerofgns. 


1 


Lignite 


Camden, Arkansas 


11,386 


22. 3 


2 


Bituminous 


Washington County, Penn- 

svlvania. 


9,880 


16.9 


3 


do 


do 


9,920 


16.1 


4 


do .. 


do 


10, 120 
10, 160 


18. 36 


5 


Cannel 


Beaver County, Pennsyl- 


22.5 






vania. 






6 


do 




12,540 


30.53 


7 


Bituminous 


Upper Monongahela 
River, Pittsburg Gas Co. 


9, 500-10, 000 


16. 


a 8 


do 


Silkstone seam, York- 
shire, England. 


10,000-11,000 


15-17 


9 


do 


Newcastle, England. 
(Average 3 typical coals. ) 


10, 760 


16.2 


10 


do 


South Yorkshire, England. 


11,000 


17. 


11 


do 


Derbyshire, England 


10, 500 


15. 


I: 


Cannel 




12,350 


31. 







i8-12, Thorpe, Dictionary of Applied Chemistry, Vol. II. 



It will be seen from this table that the Camden lignite is superior, 
both in yield and in candlepower of gas, to the standard bituminous 
coals of Pennsylvania and England, and that as a gas producer it is 
inferior only to the best cannel coals. 



A RECONNAISSANCE FROM PYRAMID HARBOR TO EAGLE CITY, 
ALASKA, INCLUDING A DESCRIPTION OF THE COP- 
PER DEPOSITS OF THE UPPER WHITE 
AND TANANA RIVERS 



AI.FRKJ) IIlfLSK 15 HOOKS 



CONTENTS, 



Page 

Introduction 337 

Itinerary 337 

Previous explorations 340 

( ieography 344 

Coast line - 344 

Orographic features. 345 

( loaal Range - 345 

St. Elias Range 345 

Nutzotin Mountains - - 346 

Yukon Plateau '. 346 

Drainage 347 

( 'hilkat River 347 

A Lsek Basin 348 

White River Basin 350 

Tanana Basin 35] , 

Fortymile River 353 

Physiographic notes 353 

Geology 356 

Gneissie series 356 

Kotlo series 357 

Greenstone schists 358 

Nutzotin sei-ies 359 

Intrusives 360 

Tertiary rocks 362 

T( >k sandstones 362 

Tertiary effusives 362 

Pleistocene deposits 363 

Sediments 363 

Effusives 364 

Glacial phenomena 364 

Volcanic tuff 365 

Ground ice 366 

Table of hypothetical correlations 367 

Summary of geology 368 

Mineral resources 373 

Gold 373 

Porcupine gold district 374 

Fortymile gold region 376 

Copper 377 

Rainy Hollow copper deposits 378 

Kletsan copper deposits :!7!i 

Tanana-Nabesna copper deposits 381 

Development of copper 382 

( !oal 3»2 

333 



33-i COMPOSITION OF THE COAL. 

Page. 

Routes and methods of traveling 383 

Dal ton trail 384 

Routes to the Upper White and the Upper Tanana 384 

Railway routes 386 

Timber ..." 387 

Game 387 

Climate 388 

Inhabitants 388 

Natives 388 

Whites 390 



ILLUSTRATIONS. 



Plate XL, 

XLI. 

XLI1. 
XLI II. 

XLIV. 

XLV. 
XLVI. 

XLVII. 

XLVIII. 

XLIX. 

L. 

Fig. 21. 



Page. 
Map showing route from Pyramid Harbor to Eagle City, and 

location of gold and copper deposits so far as determined 338 

A, Pleasant Camp and Jarvis Glacier from Dalton trail; B, Upper 

Tatshenshini Valley, showing benches along valley slope. . . 344 

Mountain ranges of Central Alaska 346 

Topographic map showing route from Lynn Canal, via headwaters 

of White and Tanana rivers, to Eagle City In pocket 

A, Dissected Yukon Plateau, near camp; elevation about 4,700 
feet, looking northwest; B, Dissected Yukon Plateau, near 

camp, elevation about 4,700 feet, looking north 348 

A, O'Connor Glacier from Slims River Valley; B, Moss-covered 

plateau in foreground; Mount Natazhat in distance 350 

A, View looking northwest across the Donjek, down the valley of 
the Koidern River, showing low divide between the Koidern 
and the Donjek; B, View looking across the Donjek, .showing 

canyon on the right 354 

Geological reconnaissance map of parts of Alaska, British North- 
west Territory, and British Columbia 356 

Profiles of St. Elias Range and Yukon Plateau, with geology so 

far as known _". . . 368 

Sketch map showing location of Porcupine gold district 374 

Sketch map showing location of Kletsan copper deposits 380 

Sketch map showing former drainage channel 355 

335 



A RECONNAISSANCE FROM PYRAMID HARBOR TO 
EAGLE CITY, ALASKA, INCLUDING A DESCRIPTION 
OF THE COPPER DEPOSITS OF THE UPPER WHITE 
AND TANAN A RIVERS. 



By Alfred H. Brooks. 



INTRODUCTION. 

In the spring of 1899 I was detailed to accompany an exploring 
expedition which was to proceed from Pyramid Harbor, on Lynn Canal, 
to Eagle City, by way of the headwaters of White and Tanana rivers, 
and which was to make such surveys along the route of travel as time 
permitted. The party was constituted as follows: William J. Peters, 
topographer, in charge; Alfred H. Brooks, geologist; Gastrow S. 
Phillip, topographic assistant; and Thomas M. Hunt, Ed. Brown, and 
Joseph Cahill, camp hands. To Mr. Phillip and to the three camp 
hands Mr. Peters and I wish hereby to acknowledge our indebtedness, 
for the success of our expedition was in a large measure due to the 
untiring and faithful service rendered by these four men. 

The following report is only a hasty summary of the results of our 
investigations. A prolonged illness and the stress of other work has 
prevented me from working up the held notes in detail. The facts 
that much of the region is so little known and that there is at the 
present time much interest in the copper deposits are believed to be 
sufficient excuse for publishing an incomplete report. It has been my 
aim to give such facts and conclusions as may be of practical value 
rather than to attempt a technical treatment of the large amount of 
matter on hand. 

ITINERARY. 

The party assembled at Pyramid Harbor on May 21, and five days 
later started inland. One hundred days' provisions and the equipment 
were packed on 15 horses, while the 6 members of the party walked 
(see PI. XL, XLIII). Our route lay up the broad valley of the Chilkat 
as far as the Indian village of Klukwan, just north of which runs the 
present (1900) provisional boundary line between the United States 

21 GEOL, FT 2 22 337 



338 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

and the Canadian possessions. At Klukwan our course turned west- 
ward up the Klehini River, a west fork of the Chilkat, and on May 
28 we reached Pleasant Camp, some 40 miles from the coast. A 
Canadian custom-house and the Northwest mounted police post are 
situated there, which was then (1899) considered the conventional 
international boundary. The spring of 1899 was unusually late, and 
we were forced to wait at Pleasant Camp about three weeks before 
the trail opened. 3 A part of this time was spent in studying- the 
geology of the neighborhood, but the presence of considerable snow 
made traveling difficult and rendered the work unsatisfactory, because 
so many of the outcrops were covered. 

On dune '21 we left Pleasant ('amp by the Dalton trail, which, leaving 
the Klehini River, crosses a high spur and then descends again to Rainy 
Hollow . at the headwaters of the same river. I lere a delay of a day to 
rest our horses enabled me to pay a hasty visit to some newly discov- 
ered copper deposits in the neighborhood. 

Beyond Rainy Hollow the trail crosses a divide to a tributary of the 
Chilkat and then leads across a second divide to the headwaters of the 
Chilkat. Beyond that it leaves the Lynn Canal drainage and descends 
to the Tatshensbini River, an east folk of the Alsek. 

On June 1'."' we reached the Tatshensbini River, at a point opposite 
Dalton House. Here a day was spent in ferrying our outfit across the 
river in Indian canoes and in swimming our horses. At Dalton House 
there is a trading post, a Northwest mounted police post, and near at 
hand a large Indian village. 

On June 30 we left the post, and with it Left behind us the last vestige 
of civilization. Up to this point we had followed the Dalton trail, but 
this now turned northward toward Lake Dezadeash. Continuing in a 
westerly direction, we reached the Kaskawulsh River, a west fork of 
the Alsek, on July l.">." Two days were spent here in building a boat 
and in getting the outfit and horses across the river. 

On July IT we crossed the moraine of the O'Connor Glacier, 8 which 
occupies a divide between the Alsek and White River waters and which 
drains in both directions. Two days later we reached the upper end 
of Lake Kluane, where we were forced to build another boat for 
ferrying across the Slims River. Our route led us along the shores 
of the lake for several days, and we then crossed a low divide to the 
Donjek River, which we reached on July 31. The fording of this 
turbulent stream proved a difficult and dangerous task and threatened 

i We are indebted to Dr.S.M.Frazer, of the Northwest mounted police, for many kindnesses shown 
us during our delay at the post, of which he was in command. 

son the Kaskawulsh we met Messrs. D. D.Garveyand J.J. Haley, two prospectors who had come 
fromYakutat Bay. We are indebted to them for much information about the country, and especially 

for a sketch map Of a part of the Alsek dra liage basin. 

'This glacier was named after Capt. J. O'Connor, who crossed ii in I898and furnished uswitha 

sketch map of his route. 



U. S. GEOLOGICAL SURVEY 




LEGEND 
ROUTE OK EXPEDITION ( NUMBERS REFER TO \\ 



TWENTY-FIRST ANNUAL REPORT PART II PL. XL 



ROITK FROM PYRAMID HARBOR TO EAGLE CITY' 

AND 

LOCATION OF GOLD AND COPPER DEPOSITS AS FAR AS DETERMINED 




BBOOKS.] ITINKKAWY. 339 

ii- with the lossof <»ur Leader and a horse, who were swept downstream 
by the madly rushing current. We were much relieved when the 

entire expedition reached the west hank in safety. 

On August 6 we reached the Klutlan Glacier, which we attempted 
to cross, but were forced to turn back because of the precarious footing 
winch it ottered our horses. The river below the glacier was almost 
as dangerous to cross as the Donjek. hut we passed it in safety. 

We remained near Kletsan Creek 1 two days to afford time for a hasty 
examination of the copper deposits, and on August 12 reached the 
White River. We followed the AVhite nearly up to its glacial source, 
and then, turning westward, laid our course for a low divide, beyond 
which we hoped to find Tanana waters. We crossed this divide and 
on August 14 reached the glacier in which the Tanana River heads. 
Thence we made our way across a second divide to the Nabesna, a west 
fork of the Tanana. We followed the Nabesna downstream for about 
20 miles, and then, taking a northwesterly course, reached the Tanana. 
near the mouth of the Tetling River, on September 1. On September 
3, having built a boat and ferried our outfit and swum our horses across 
the Tanana, we continued our course in a northerly direction toward 
Fortymile River. After traversing the flat swamp- and lake-covered 
valley bottom for a few miles we reached the north wall of the valley, 
which rises by a gradual slope. The watershed lies close to the Tanana 
Valley, and to the north we followed a stream occupying a shallow 
valley. About 30 miles north of the Tanana this stream makes an 
abrupt turn to the east and probably Hows into the White River. We 
continued on our northerly course and after crossing a second divide 
reached a broad valley which is tributary to Dennison Creek, a branch 
of the South Fork of Fortymile. We reached the South Fork of the 
Fortymile on September 10, and having renewed our supply of pro- 
visions,- which had run rather low, continued on by trail to the mouth 
of Steele Creek. Here a boat was procured and four of the party, 
including the topographer and the geologist, continued the journey to 
Eagle City by water, while the other two men brought the remaining 
7 horses by trail. On September It; the entire party assembled at 
Eagle City. 

Our route was over 600 miles in length, and we made the journey 
in sixty-six days. Of this distance we were obliged to chop a trail for 
about lo miles. We started with 15 good horses and 8 of them were 
left by the wayside, most of them being shot because they were too 
weak to keep up with the others. 

i We there met E. J. Cooper and H. \. Hammond, who had come with a pack train from Copper 
River. Mr. Cooper gave us some valuable information about the region. 

2 In this connection we are indebted to Mr. Thomas Marl in, of Napoleon Creek, who. true to the tra- 
ditions oi the Alaskan pioneers, received us hospitably and shared with us what provisions \w had. 



340 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

PREVIOUS EXPLORATIONS. 

It is not my purpose to attempt a complete history of the previous 
explorations of the region traversed by our party. To give an account 
of the explorations and mapping of the southeastern part of Alaska 
would be almost to write a history of the explorations in the northern 
Pacific Ocean since the middle of the sixteenth century. 1 

The head of Lynn Canal is said to have been first explored in 1796 
by Shultz. an employee of the Russian- American Fur Company. 2 Since 
the purchase of the territory in 1867 the United States Coast and Geo- 
detic Survey has steadily progressed in the mapping of the coast line 
and adjacent areas. The investigations of Professors Pratt and David- 
son in connection with that Bureau have contributed much to our 
knowledge of this region. The reports and maps will be found in the 
publications and maps of the Coasl Survey. In recent years the work 
of the International Boundary Survey has extended the mapping of 
the mould a ins adjacent to the coast of southeastern Alaska. The studies 
and explorations of Mr. John Muir. Profs. I. C. Russell, H. Fielding 
Reid, and (I. Frederick Wright have added much to our knowledge of 
the glaciers of the Alaskan coast. 

1877. Lieut. ('. E. S. Wood/ LT. S. A., made a journey into the 
Mount Fairweather region with a party of native hunters, and was 
probably the first white man to see (ilacier Bay. 

I,s7'.>. Prof. John Muir' and Rev. S. Hall Young visited the Muir 
(ilacier and explored lev Hay. They were the first white men to explore 
(ilacier Bay. 

1872-1879. Arthur Harper made several prospecting trips la+n the 
White and Tanana river basins." 

1880. Captain Beardslee 8 visited Glacier Bay in the steamer Favorite, 
and Ensign Ilanus made rough surveys of the lower end of the bay. 

1880. Mr. John Muir made a second visit to Glacier Bay. 7 

1882. Dr. Arthur Krause made explorations of ChilkootandChilkat 
passes. 8 



i Those interested in this mattei are referred to Alaska and its Resources, by William II. Dull; Ban- 
croft's History .ii Alaska; and Report of the Population, Industries, and Resources of Alaska, by Ivan 
Petroff. Torn bibliography of publications relating to Alaska, see Pacific Coast Pilot, Appendix 1, 
U. S. Coast and Geodetic Survey, 1879, William H. Dall and Marcus Baker. 

*Dall,op. cit, p. 817. 

3 Among the Thlinkits: The Century Magazine, .Inly, 18H2. 

4 The discovery of Glacier Bay. by John Muir: The Century Magazine, .Tun.-, 1895. 

6A reconnaissance in the White and Tanana river basins: Twentieth Aim. Kept. U. S. Geol. Survey, 
Pt. VII, pp. 435 and 437. 

"Senate Ex. Doc. No. 105, second session, 16th Congress 

"The discovery of Glacier Bay, by Kliza Ruhama Scidmore: Nat. Geog. Mag.. Vol. VII, April, 1896, 
p. 143. 

8 Deutschc Geographische Blatter, Bd. V, Heft l, W2, with map. Zeitschrift fur Krdkunde, Berlin, 
Bd. XVIII. 18X3. Yukon district and British Columbia, by G. M. Dawson: Geol. Surv. Canada, 1887-88, 
p. 181 B. 



brooks.] PREVIOUS EXPLORATIONS. 341 

1883. Lieut. Frederick Schwatka crossed the Chilkoot Puss and 
descended the Lewes and Yukon rivers, making surveys en route. 1 

1885. Lieut. Henry T. Allen, IT. S. A., with a small party, ascended 
the Copper River, crossed to the Tanana by the Suslota Pass, and 
floated down that river to its mouth. 2 

1886. Lieut. Frederick Schwatka, accompanied by Prof. William 
Libbey and Lieut. H. W. Seton-Karr. and two camp hands, made an 
attempt to ascend Mount St. Elias, and reached an elevation of T.i'iiu 
feet. 3 

1886. Prof. G. Frederick Wright* devoted a month to the study 
of the Muir Glacier. 

1888. W. H. and Edwin Topham, with George Broca and Wil- 
liam Williams, ascended the southern slope of Mount St. Elias to a 
height of 11,460 feet. 6 

1888. William Ogilvie, Dominion land surveyor, made surveys 
from D\ea, on Lvnn Canal, to the International Boundary, on the 
Yukon/ 

1888. Dr. G. M. Dawson studied the geology of the Lewes River, 
Chilkoot Pass, and the head of Lynn Canal. 7 

1890. Prof. I. C. Russell, with Mark B. Kerr, topographer, and 
six camp hands, attempted the ascent of Mount St. Elias, under the 
joint auspices of the National Geographic Society and the U. S. Geo- 
logical Survey. 8 

1890. Prof. H. F. Reid, with five companions, spent the summer in 
studying and mapping the region about Muir Glacier. 9 

1890. Messrs. S. J. Wells, E. J. Glave, and A. B. Schanz, on an 
expedition organized by Frank Leslie's Weekly, ascended the Chilkat 
River and. crossing the coast range, explored Lake Kusawa (then 
called Lake Arkell). 1 " There the party divided, and Schanz and Wells 
proceeded to the Yukon, while Glave, accompanied by Jack Dal ton, 
crossed the divide to the Alsek waters and proceeded down that river 
to the coast. 

'Military reconnaissance in Alaska, 1883, with maps; second series: Senate Ex. Doc. No. '-', Forty- 
eighth Congress. 

= A report mi an expedition to the Copper, Tanana, and Koyukuk rivers, in the Territory of Alaska, 
in the year 1885. This report includes maps of three rivers, Which up to 1898 were the basis oi all 

maps of in. region. 

"Shores ami Alps of Alaska, by H. W. Seton-Karr: New York Times, October 17, 1886. The expedi- 
tion of the New York Times, by Frederick Schwatka: The Century Magazine, April, 1891, \\ iih sketch 
map. 

<TheIce Age of North America, 1889; chapter III. 

'Scribner's Magazine, April. 1889; Upine Journal, August, 1889. 

"Klondike Official Guide, 1888. 

7 Ann. Kept. Geol. Sttrv. Canada, Vol. IV, 1SS8-89. I'art H, with maps. 

M-'.xpedition to Mount st. Elias, by I. <'. Russell: Nat. Geog. Mag., Vol. in. 1891-92, with maps. 

'Studies ol the MuirGlacier, by II. F. Reid: Nat. Geog. Mag., Vol. IV. 1892 98. Noteson the geol 
ogy in the vicinity of the MuirGlacier, by II I'. Gushing; Nat. Geog. Mag., Vol. IV. 1892-98. Glacier 
Hay and its glaciers [with maps]. Sixteenth Ann. Kept. I'. S. Geol. Survey, 1896, Pt. I. pp. 421-461. 

i Kepoi i on the population and resources of Alaska, 1891, Eleventh census, p. v. 



342 FKOM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

1890. Mr. S. J. Wells. 1 of the Frank Leslie Exploring Expedition, 
with one companion, crossed from Fortymile to the Xanana and con- 
tinued down that river to its mouth. 

1891. Prof. I. C. Russell, with a party of six men, made a second 
attempt to reach the summit of St. Elias, again under the auspices of 
the I". S. Geological Survey and the National Geographic Society. 2 
At an elevation of 11.500 feet they were forced to turn back because 
of severe storms. 

1891. Lieut. Frederick Schwatka. U. S. A., Dr. C. Willard Hayes, 
of the I'nited States Geological Survey, and a prospector named Mark 
Russell, reached the head of White River by an overland route from 
Fort Selkirk. 3 They crossed Skolai Pass and reached the coast by 
way of Copper River. 

L891. K. .1. Glave and .lack Dalton, with four pack horses, followed 
up the Chilkat River, crossed the two forks of the Alsek, and reached 
the upper end of Lake Kluane. then returned to the coast by the same 
route. They were the first to use pack horses in Alaskan explorations. 4 

L896. -lack Dalton.' who accompanied E. .1. Glave in 1890 and 1891, 
established a trail now known as the Dalton trail, from Pyramid Har- 
bor to the mouth of the Xordenskiold River. He had some years 
before established trading posts at Pleasant Gamp on the Klehini, and 
at Dalton House on the Tatshenshini. He has made several trips into 
the White River country from Pyramid Harbor. 

1896. .1. E. Spurr." assisted by II. B. Goodrich and K. G Schrader, 
studied the geology of the Yukon gold district, paying especial atten- 
tion to the Fortymile and Birch Creek districts. 

L897. Prince Luigi, with a strong, well-equipped party, succeeded 
in reaching the summit of Mount St. Elias. 1 

L897. d. .1. McArthur made survey of Dalton trail, running from 
Pvramid Harbor t<> the mouth of Xordenskiold River. 8 



t Report "ti tin population and resources of Alaska: Eleventh < vnsn-. isn:!. inn previous publica- 
tion (A reconnaissance in the White and Tanana River basins: Twentieth Ann. Rept. TJ. S/ Geol. 
survey i I unfortunately omitted to mention t li i- exploration of Mr. Wells. 

- cond expedition to Mount si Elias, bj I C. Russell: Thirteenth Ann.Rept.1 .8. Qeol. Survey, 
Part II [with maps]. 

■An expedition through the Yukon district [with maps] bj C. Willard Bayes: Nat. Geog. Mag., 
pp. 117-162, May 15, 1892. 

< Pioneer pock horses in Alaska, by E.J. Glave: The Century Magazine, Vol, XLIV, Nob. 5 and 6, 

September and October, 1892. 

r, Mr. Dalton. of Pyramid Harbor is the best Informed man of the region, and we are much indebted 

to him for information furnished us. 

•Geology of the Yukon gold district, by Joeiah Edward Spurr, with a chapter on the history and 
condition of the district, by Harold Beach Goodrich: Eighteenth win. Kept- U.S. Geol. Survey, 
Pt. Ill, pp. 87-392. 

■ I.;. SpedizionediS. A. R. ilDucadegli Abruzzial Monte Sant' Elia (Alaska), 1897; Ulrico 1 pli 

Milano, 1900. The ascent of Mount St. Elias by H. R. H. Prince fjuigi Amedeo; Archibald Constable 
and Co., Westminster. 1900. The ascent of Mount. St. Elias: Sierra Club Bulletin, Vol. II, No. S, 
Jan., 1898. 

-This BUTvey i- embodied m Dawson's map ol portion of the Yukon district. Sheet III. corrected to 
January, 1S98: Geol. Surv. Canada, 1888. 



PREVIOUS EXPLORATION-. 343 

L898. J. B. Tyrrell studied the geology along the route of the Dal-' 

ton trail. He also made explorations westward from Hutshi to the 
White River. 1 

L898. Lieut P. <i. Lowe. U. S. -V.. with a pack train, went from 
Valdes t<» Fortymile post on the Yukon, byway of the Copper River. 
Tie crossed the Tanana aear the mouth of the Tetling River." 

Isms. ("apt. W. R. Abercrombie ascended the Copper River to 
Mentasta Pass. 

L898. K. C. Barnard. United States Geological Survey, mapped 
the topography of the Fortymile quadrangle. 4 

1898. Russell L. Dunn visited the Dalton trail region and pub- 
lished some geological and mining note-." 

L898. W. J. Peters and Alfred H. Brooks, with a small party, 
ascended the White River and its tributary, the Snag River, in canoes, 
then portaged across to Tanana water- and followed the river of that 
name to its mouth. They made surveys along the entire route. 

1899. Oscar Rohn. employed by the United States Army as topog- 
rapher, ascended the Chitina River with pack train to the foot of the 
Nizina Glacier. He then, with one companion, crossed by this glacier 
to the head of the Tanana. and continuing westward they crossed the 
divide to the Xahesna. and then returned to the coast by way of the 
( opper River. 7 

189T-18U9. The Klondike excitement of these two years led to 
much exploration in this region by prospectors hunting for gold. 
Baltics entered the region from almost every point of the compass. 
Some crossed the glaciers from Yakutat Bay to the Alsek, and ascended 
that stream, while some left the coast by way of Copper River and 
reached the "White River by way of Skolai Bass. Others again came 
in from the Lewes River, and many along the well-worn Dalton trail. 
There are no authentic data relating to most of these parties. Here, 
a- elsewhere in tins northern region, in probably not a few ease-, bleach- 
ing bone- are the only record- left to mankind of the indomitable will 
and unheralded heroism of the American prospector. 

i Summary Report, 1888, Geol. surv. Canada, pp. 36-^16. 

-A narrative of t Hi- expedition, together with a -ketch map. is published in Reports of explora- 
tions in the Territory of Alaska, 1898; War Department, Adjutant-General's Office, No. XXV, July, 
1899. 

>No BUrvej - were made by this expedition, but a narrative is published in Reports of explorations 
in the Territory of Alaska, 1898; War Department, Adjutant-General's Office, No. XXV. .Inly, 1899. 

• Explorations in Alaska in 1898, Map 10, p. 76; 0. S. Geol. Survey. 1899. 

•The country of the Klondike: Mining and Scientific Press, San Francisco, Cal., 1898; Vol. I.xxvn 
1999,2000, Oct 22-29, and Nov. 25. 

•The White River and Tanana expedition, by W.J. Peters and Alfred H. Brooks: Explorations In 
Alaska, 18 - - irvi L899 \ i conns ssance in the White and Tanana river basins in 

tffred H. Brooks: Twentieth Ann Kept U. S. Geol. Survey, I't. VII, 1900. 

i An account of this expedition, with map, will be found elsewhere in this volume. 



344 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

GEOGRAPHY. 

The region on which our investigations throw more or less light is 
approximately blocked out by the Lynn Canal on the east, by the St. 
Elias Range on the south, by the 142d meridian on the west, and by 
the Yukon on the north (see Pis. XLI and XLII). It majr roughly be 
regarded as a parallelogram along whose southern and western sides 
our r*oute of travel lay and which lies for the most part within the Yukon 
Plateau belt. 1 While the investigations of L899 were limited to a nar- 
row zone along this route, 3'et a previous familiarity with the section 
from Lynn Canal across the Coast Range and down the Lewes to the 
Yukon, as well as previous studies along the Lower White and Tanana 
rivers, together with a libera] use of reports of the published work of 
others, will enable me to suggest some correlations which would 
hardly he warranted by the work of one season. 

COAST LINE. 

Lynn Canal, a deep indentation of the coast line, is one of the many 
tidal fiords which are so characteristic of the southeastern Alaskan 
coast and which indicate a drowned topography. Along the canal 
the steep slopes of the mountain rise precipitously, here and there inter- 
rupted by a bench marking a forme]- level of depression.' 

At the mouths of the larger rivers broad deltas have been built out 
into the fiord, and offer opportunities for settlements along a shore 
which is usually very precipitous. Such plains exist at the mouths of 
theChilkat. Skagway. and Dyea rivers, and have been utilized for hab- 
itation. The upper pari of Lynn Canal is divided by a narrow neck of 
land into two embayments, called Chilkool and Chilkat inlets. The 
larger, containing Davidson Glacier, discharges into Lynn Canal near 
the mouth of Chilkool Inlet, and the drainage of numerous other glaciers 
which do not reach tide water finds its way to Lynn Canal. The general 
aspect of the country near the canal is rugged and forbidding. 

West of Lynn Canal is another fiord, Glacier Bay, one of the best 
known points in Alaska, annually visited by many tourists, who come 
to view its famous glaciers. Cross Sound connects these waters with 
the Pacific. West of Cross Sound, as far as Cape Suckling, which lies 
just east of Copper River, the (Tagged peaks of the St. Elias Range 
rise precipitously from near the coast and many glaciers clothe the 
mountain slopes, frequently fronting the sea. This stretch of the 
coast is remarkably even, its uniformity being broken only by Lituya 
Bay, Dry Bay at the mouth of Alsek, and by the larger indentation 
known as Yakutat Bay. 



in the White and Tanana river basins, Alaska, 1898: twentieth Ann. Repl U.S. 
Geol. Survey, I't. VII, pp. 425-494. 

•-At Pyramid Harbor benches were obsnv.<l al about 100, 800 100, and 700 feet above tide water 




A. PLEASANT CAMP AND JARVIS GLACIER FROM DALTON TRAIL. 




Jl UPPER TATSHENSHINI VALLEY, SHOWING SENCHES ALONG VALLEY SLOPE. 



BB00K8.] MOUNTAIN RANGES. 345 

OROGRAPHIC FEATURES. 1 
COAST RANGE. 

North of Lynn Canal a chain of mountains, called the Coast Range, 
separates the Pacific and Yukon waters. Near Dyea the watershed is 
only about 20 miles from tide water. The range extends southeast- 
ward, close and parallel to the coast line, into British Columbia. North- 
west of Chilkoot Pass the range trends inland, and finally loses its 
distinctive character and merges into the Yukon Plateau. Some moun- 
tains lying west of Lake Dezadeash, which have been called the Dalton ; 
Range, possibly represent an extension of the Coast Range uplift. 
These mountains, as Dr. Hayes* has shown, form a broad, elevated 
mass, having no dominant range. Near Lynn Canal, from an elevation 
of about 5,000 feet, the range is seen to be made up of innumerable 
peaks and minor ranges, whose crests rise to about the same elevation 
and show a remarkably even sky line. The Coast Range does not 
everywhere form the watershed between the Pacific and interior waters, 
for a number of rivers, such as the Stikine and the Taku, have their 
sources north of the Coast Range. 

ST. ELLAS RANGE. 

West of Lynn Canal, where the Coast Range passes inland, the 
St. Elias Range occupies the continental margin, and is abroad moun- 
tain chain stretching to the northwest of Cross Sound and lev Strait 
(sec PI. XLII). To the southeast of these two straits, which lie nearly 
at right angles to the direction of its axes, the St. Elias Range is 
partially submerged, and is represented by the highlands of the Alex- 
ander Archipelago. Northwest of Cross Sound lies the Fairweather 
group of mountains, and still farther to the northwest the range 
increases in ele\ ation, culminating in the peaks of St. Elias and Logan 
and probably others which have not been determined. To the north- 
west of these peaks the range, as Dr. Hayes* has shown, bifurcates, 
and the most northerly of the two chains, called the Skolai Mountains 
on the accompanying maps, forms the watershed between the Chitina 
on the south and the Tanana and Nabesna rivers on the north, and also 
•includes the Wrangell group of volcanoes. The southern chain 
approaches the coast and merges into the Chugach Range, 5 on the 
Lower Copper River. The St. Elias Range proper has a length of 
about 300 miles and an extreme width of about 70 miles. From Cross 



"See Pis. XLII and XLIII. 

aCompare topographic map oi l>aitc>n trail, by .1. J. McArthur. 
1 Expedition through the Yukon district: Nat.Qeog. Mag., Vol. IV, p. 128. 
'Op. (it,, p. 129. 

»A reconnaissance ol a partof Prince William Sound and theCopper River district, Alaska, is 
F. C. Schrader: Twentieth Ann. Kept. U.S.Qeol. Survey, I't. VII, pp. 841-423. 



34<) FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

Sound to the Copper River it is a continuous mountain barrier except 
for the broad valley of the Alsek, which cuts completely across its 
axis. To the south of our route of travel from Lynn Canal to the 
White River we could see the bewildering muss of snow-chid moun- 
tain chains and peaks which make up this great range. The topog- 
raphy is cragged, and innumerable glaciers occupy the higher valleys, 
fed by extensive neves. 

MTZOT1N MOUNTAINS. 

In a previous report I have described the Nutzotin Mountains, 
from which the Nabesna and Tanana rivers emerge, and whence they 
debouch on the broad gravel plain of tin 1 Upper Tanana Valley. 
From the Nabesna these mountains have a southeasterly course and 
extend through to "White River, but in the last 20 miles they decrease 
very much in elevation and become a low range of hills. The exten- 
sion of the axis of this range to the southeast of the White would 
coincide with mountains to the north of Lake Kluane. 'hicli attain 
considerable altitude. These mountains, so Ear as we could observe, 
serin to constitute a more or less well-defined range as far as the Kas- 
kawulsh River, beyond which they probably merge with the Yukon 
Plateau, though the mountains lying immediately north of the Chilkat 
River may belong to the same uplift. To the northwest of the 
Nabesna River this range is continued by what are called the Mentasta 
Mountains, which, in their northwesterly extension, join the great 
Alaskan Range. The extreme width of this chain is about 30 miles 
and its highesl peaks measure 10,000 or 1 L,000 feet. 

The above description of the ( loasl and St. Elias ranges and Nutzotin 
and Mentasta mountains includes all the mountain ranges proper 
embraced in the areas under discussion. Within the plateau belt to 
be described below mountains which rise above the general elevation 
of the plateau are not uncommon. In some cases a series of such 
mountains, arranged more or less linearly, suggests a synchronous 
uplift, but such mountains are usually separated by plateau areas, and 
can not be regarded as definite ranges. Mountains of this class are 
common between the Tanana and the Yukon. The Kechumstuk Hills' 
belong to this category. 

v i Ron PLATEAU.' 

North from the Coasi and St. Klias ranges stretches the great 
interior upland which has been called the Yukon Plateau." This is 
a dissected upland, whose remnants show an even sky line and mark a 
gently rolling plain, which slopes toward the northwest. In it the larger 

1 Often culled the Razor-back Divide h 

-The relation oi the plateau and tie mo mtain ranges is shown in tie- profiles mi PI. XL VIII. 
<cc PI. XLIV. .1 and B, and PI. XLV, B. 



U. S. GEOLOGICAL SURVEY 




TWENTY-FIRST ANNUAL REPORT PARTIIPL.XLI 



MOUNTAIN RANGES OF CENTRAL ALASKA 

Topography by LI S. Geological Survey, U.S.CoasI and Geodetic Survey 
[international Boundary Survey, and Geological Survey of Canada. 




j..«'; 



wm< 



3 






OHILKAT RIVER. 347 

rivers have cut broad valleys, the relief varying from 1,000 to 3,000 
feet. This plateau has been traced from the region of the Upper 
Liard, in British Columbia, to the Lower Tanana, and thence to the 
big bend of the Yukon. In this distance it decreases in elevation from 
5,000 or 6,000 feet in British Columbia to 2,500 feet near its north- 
western limit in Alaska. While in general the surface of the plateau 
slopes northwest there are irregularities in the plain marked by the 
plateau remnants, which, it has been suggested, may be due to warp- 
ing. 1 The Yukon Plateau was first named by Dr. Hayes and has 
been described in more or less detail by various writers. 2 

DRAINAGE. 
CHILKAT RIVER. 

Of the three drainage basins which are in part included in this area 
that of the Chilkat Riven- is the smallest. The river rises in a broad 
depression, which forms the divide between it and the Alsek River 
system. It has a southeasterly course, and in a distance of about 60 
miles empties into Chilkat Inlet, an embayment of Lynn Canal. 

In the upper part of its course the Chilkat River flows through a 
canyon or canyon-like valley which is incised in an older valley floor. 
The bottom of the older valley is marked by benches which extend 
from either side of the canyon to the base of the mountain slopes. 
About It) miles above the Indian village of Klukwan the character of 
the Chilkat Valley changes. From this point to the coast the river is 
diversified into numerous channels and wanders over a broad gravel- 
filled valley bottom. This part of the valley probably represents a 
former inland extension of the tidal fiord, which has been filled with 
gravel and silt. The valley slopes rise abruptly, with an occasional 
bench, the highest one observed being about 1,000 feet above the 
water. 

At its mouth the river has a broad delta which occupies the head of 
the inlet, and is gradually encroaching upon it. The delta is extended 
seaward by broad silt flats which are covered at high tide. The two 
most important tributaries are the Takhin and Klehini, both flowing 
from the west. The. former joins the Chilkat 10 miles from the inlet, 
and the latter some 10 miles above. The Takhin rises in a glacier 

1 A reconnaissance in the White and Tanana river basins. Alaska, in 1898: Twentieth Annual Kept. 
U.S. Qeol. Survey, Pt. VII, p. us. 

-Tin' Yukon district, by c Willard Hayes: Journal of school Geography, Vol. I. No. 8, pp. 236--241, 
on the late physiographical geologj of the Rocky Mountain region and Canada, with special refer- 
ences to the Changes in elevation and to the history of the Glacial period, by Geo. M. Dawson: 

Trans Roy. Soc. Canada, 1890, Vol. VIII. Report on an exploration in the Yukon and MacKenzie 

basins, Northwesl Territory, by R. fi. McConnell: Ann. Kept. Nat. Hist. Survey of Canada, Part D, 
Vol. IV, 1888 89. Geology Of the Yukon gold district, by .1. E. Spurr : Eighteenth Ann. Kept. !\ s, 
(ieol. Survey, Pt. Ill, pp.259-260. The Yukon district, by Alfred II. Brooks: Explorations in Alaska 
in 1898; (J. S.Geol. Survey, 1899, pp. 85-100. A reconnaissance in the White and Tanana river basins, 
Alaska, by Alfred II. Brooks: Twentieth Ann. Kept. C, s. i Ieol. Survey, Pt.VII.pp. 125-494. 



348 FROM PYEAMID HARBOR TO EAGLE CITY, ALASKA. 

which is part of the great snow and ice field north of Glacier Bay. 
The Klehini, up which our route lay, has its source in a broad, flat 
divide, similar in character to that at the source of the Chilkat. Up 
to Pleasant Camp the Klehini River occupies a gravel-floored valley, 
similar to that of the Lower Chilkat and showing- similar benching. 
Above Pleasant Camp it flows through a narrow rock canyon which 
has been incised in an older valley floor. 

An examination of the accompanying map (PI. XLIII, in pocket at 
end of volume) will show that the headwaters of the Chilkat, Glave, 
and Klehini rivers are separated by very broad, flat divides. This 
broad depression, below which the rivers have cut sharp canyons, 
evidently marks an old water course which has been robbed of its 
drainage b}>- the Chilkat and its tributaries. 

The relief in this drainage basin is from 3,000 to 7,000 feet, and the 
divides stand at about 3,000. Small lakes are not uncommon, and so 
far as observed are the result of an interruption of the drainage by 
glacial action. The rivers of this system are all more or less glacier- 
fed streams and are. as a rule, turbid. They are swift flowing and, 
except for the lower course of the Chilkat. unnavigable. Their shift- 
ing channels ami bowlder-covered bottoms usually make them difficult 
to ford. 

ALSEK BASIN. 

The Alsek River forks some -b> miles above its mouth. The eastern 
fork, called the Tatshenshini. 1 lias its source, as has been described, near 
the head of the Chilkat. in its upper course it flows through a suc- 
cession of rock canyons and broad gravel-filled valleys, the latter often 
containing silt and gravel terraces (see PI. XLIY. //). Where the 
river occupies a canyon this has been incised in an old valley floor. 
Below Dalton House, the river enters such a rock canyon but a few 
hundred yards wide and probably LOO or 200 feet deep. Above the 
canyon i- a broad bench marking the old valley floor, which is several 
miles wide. Below this point the rivei has not been surveyed, and the 
only information available was obtained from prospectors. Accord- 
ing to statements and sketch maps made; by prospectors who are 
familiar with the Tatshenshini Valley, the river flows in a rock canyon 
500 or 600 feet deep for most of the distance between Dalton House 
and its mouth. Above the canyon there is said to be a bench, some- 
times several miles wide, which extends to the valley slope proper. 
This bench probably marks an old valley floor. 

'This nomenclature is in accordance with Canadian official maps, on the Yukon map, sheet i. 
issued by the surveyor-general's office of Canada, March, 1898, the name Alsek is given to a river 
which is represented to have its source near Mount Logan, and which is9hown to join the Kaskawulsh 
near the sixtieth degree of latitude. The best information obtained from prospectors would go to 
show that there is no river of such size coming in from the west, and thai it it exists at all it must he 
an unimportant tributary. This being the case, the name Alsek would apply only to the lower river, 
below the junction of the Kaskawulsh ami Tatshenshini. 

For Ala-kan nam.- see pp. IR7-509of this report. 



GCOL.1..ICAL suwE. 





£. DISSECTED YUKON PLATEAU NEAR CAMP NO. 53; ELEVATION ABOUT 4,700 FEET; LOOKING 

NORTH. 



ALSEK BASIN. 349 

The west fork of the Alsek, which is called the Kaskawulsh, has its 
source in a large, irregularly shaped lake, called Dezadeash, lying 
about 20 miles northwest of Dalton House. It leaves the lake with a 
northeasterly course, and in a distance of about 20 miles makes a sharp 
bend to the west, flowing in this direction for about 30 miles, when it 
turns to the southwest, and then keeps a general southerly course until 
it joins the Tatshenshini. 

In its upper course the Kaskawulsh 1 flows through a broad, flat 
valley, and as far as our information goes it preserves this general 
character until it enters the mountains (see topographic and route 
map, PI. XLIII, in pocket). Where crossed by the party the river 
valley has a basin-like character, is about a mile wide, and is bounded 
by low hills. It enters this basin through a constricted part of the 
valley and leaves it through a narrow rock canyon. The eastern valley 
slope rises by a scries of small terraces up to 100 feet, and then extends 
inland for several miles as a broad, level bench. These terraces are 
undoubtedly of lacustrine origin, and the lake was drained by the 
cutting down of the canyon below the basin. 

So far as known, the one large tributary of the Kaskawulsh is the 
river 2 draining the Aishihik Lake, which joins it near the point where 
it makes its southwesterly bend. The O'Connor River is another 
important tributary, which has its source in the O'Connor Glacier (see 
PI. XLV, A); and this, in turn, has a tributary of considerable size, 
which rises in the direction of Mount Hubbard and joins the O'Connor 
near its mouth. This, like the O'Connor, is a turbid stream, and has 
a glacial source. 

The Alsek River system includes a region of extremely varied topog- 
raphy. Its upper waters lie within the Yukon plateau, and here the 
valleys have been cut some 3,000 to 4,000 feet below the general level. 
The basin is drained by valleys which cut entirely through the St. Elias 
range, and here the relief must be many thousand feet, but accurate 
data are entirely lacking. The Alsek is said to be fed Tby numerous 
glaciers in that part of its course where it cuts the range. Waterfalls 
and rapids have been reported on both the lower Tatshenshini and the 
Kaskawulsh. The elevation of the Dalton House is about 2,500 feet, 
so that the Tatshenshini waters fall about that much in the distance of 
100 miles to the sea. As would be expected from this fact, the reports 
state that the river is swift and turbulent. The maps show that the 
Alsek empties into Dry Bay, which reaches almost to the base of the 
mountains. This bay 'was thus named because its bottom is uncov- 
ered at low tide. 

1 Sec map bj J.J. McArthur. 

-This is sometimes called the Jarvis River by prospectors. 



350 FROM PYRAMID HAEBOR TO EAGLE CITY, ALASKA. 

WHITE RIVER BASIN. 

The White River has been heretofore deseribed by me, in part from 
my own investigation, and in part from descriptions published by 
Dr.* Hayes. 1 The following 2 is quoted for the sake of making the 
description of the geographic features complete: 

The White River rises in the northern lobe of the Russell Glacier, which comes 
down from the St. Elias Mountains and flows east for about 40 miles nearly parallel 
with the range, and receives from it numerous tributaries. In its upper course it 
has a broad, gravel-floored valley some 10 miles in width, which gradually narrows 
down and assumes a canyon-like character. The narrow valley continues for a dis- 
tance of 20 mil,-, and then the river debouches on a broad valley lowland. This 
second basin has a length of over 75 miles anil an extreme widtli of .V) miles, while 
its floor is also composed of river gravels. It embraces not only the White River 
Valley and some of flic confluent streams, but is extended through to the Tanana 
by broad, flat valleys, while fo the east it is continued by the valley of the Nisling 
River. Here and there fche comparatively even plain of the lowland is interrupted 

by knobs, hills, and mountainous masses, which rise rather abruptly. . . . 

Some 10 miles below the mouth of Snag River the flats end abruptly and the 
White enters a narrower valley. In this part of its course the valley bottom is some 
1,300 feet below ih,' plateau surface. Terraces are found on both sides as far as the 
mouth of the Klotassin, below which they are replaced by steep granite bluffs. The 
Klotassin, which at its mouth is some hundred yards wide, is a clear-water stream 
Bowing in a broad, flat-bottomed valley. Between the Klotassin and the Katrina 

rivers the White River Valley is rather contracted, with abruptly rising walls, while 
below the Katrina it gradually widens out and continues in this form fo its junction 
with the Yukon. The valleys of both the Katrina River and La hie ( 'reek are broad 
ami flat, and they are both clear-water streams. At the junction with the White 
the Yukon makes a right-angled bend to the northeast, so that the axis of flu; White 
River Valley is extended by the Yukon below its mouth. On the Yukon, opposite 
the mouth of the White, steep bluffs rise rather abruptly some 1,400 feet above the 
river. The junctii f the two rivers is in Kritish Northwest Territory, some hun- 
dred miles above Dawson, and the total length of the White is about 200 miles. 

Throughout its course the White is a turbid, swiftly flowing stream, and it is shal- 
low, with numerous channels, and is studded with constantly shifting sand bars and 
islands. It has all of the characteristics of an overloaded stream. No current 
determinations were made on the White River, but rough estimates show currents 
of from 5 to 10 miles an hour. 

Iii the above the confluent streams of the Lower White, which are 
comparatively small, are described, but those of the upper river, with 
which I was not then familiar, are omitted. The largest tributary 
of the White is the Donjek, which rises in a large glacier fed by the 
ice-covered St. Elias Range, and. flowing in a northwesterly direction. 
joins the White some bo miles below its source. For the first 20 miles 
the Donjek has a broad, gravel-tilled valley; then, turning northward, 
it enters a canyon. This canyon is not many miles in extent, and 
where the Kluane joins the Donjek the valley broadens out again. 
The Kluane has one of its sources in Lake Kluane, which it leaves 
through a canyon-like valley. Lake Kluane is about 50 miles long, 



1 An expedition into the Yukon Basin: Nat. Geog, Mag., Vol. IV. 
2Twentieth Ann. Kept. U.S. Geo]. Survey, ft. VII, pp. M8-449. 



TWENTY-FIRST ANNUAL REPORT PART II PL. XLV 





*z3&£& 






A. O'CONNOR GLACIER FROM SLIMS RIVER VALLEY 




OUNT NATA7HAT IN DISTANCE. 



brooks.] XANANA BASIN. 351 

and occupies a part of a former valley which extended from Lake 
Dezadeash to the White, crossing the Donjek and joining the flat of 
the Middle White by the Koidern Valley. Creadon River, joining the 
Kluane from the east, occupies a part of this former drainage channel. 
Another tributary is Slims River, which has its source in the O'Connor 
Glacier (see PI. XLY. .1). The volume of the Donjek is probably 
equal t<> that of the main White River. 

The Koidern, which occupies a part of the old valley described 
above, is a comparatively small river. The Klutlan, which joins I lie 
White above the canyon, is fed by the large glacier of that name. and. 
considering its length, has a large volume of water. 

TANANA BASIN. 

The Tanana River rises south of the Nutzotin Mountains in a gla- 
cier of the same name. Near its head it is joined by two tributaries, 
nearly equal to it in size and also having glacial sources. These head- 
waters lie in a broad basin having an elevation of about 5,000 feet, 
which is connected with the White River waters by a broad gap about 
1,000 feet in elevation. The gap between the Tanana and Nabesna 
rivers is narrower, but has about the same elevation. 

Below this basin the Tanana, flowing northeastward, enters the 
Nutzotin Mountains, and here its valley is constricted for a distance 
of about 20 miles. It then debouches on the broad valley lowland of 
the Upper Tanana, here about 25 miles wide. It flows across this 
plain until it reaches the north wall of the valley, and then turns 
abruptly to the northw T est. 

The Nabesna is the largest tributary of the Tanana. It has a 
glacial source on the northern slope of the Mount Wrangell group, 
flows in a northeasterly and northerly direction, and joins the Tanana 
near the western margin of the Upper Tanana Basin. Throughout its 
course, as far as known, the Nabesna 1 flows in a broad valley, and is 
probably much older than the gorge of the Tanana. Both the Tanana 
and Nabesna are swift-flowing streams until they reach the valley low- 
land already referred to. 

I quote the following from the report on the Tanana: 2 

The broad lowland ends near the tnouth of the Tetling, where the valley is con- 
tracted to about 7 miles. West of Mount Chisana the Tanana Valley is formed by a 
series of connecting basins, possessing outlines of parallelograms. These will he 
described below, and their origin ascribed to structural lines. This basin-like char- 
acter is more or less well marked hi about the mouth of the Silok River, where the 
recession of the south wall of the valley produces another lowland, some 30 miles 
wide, and which continues to broaden out to the west. Something of the same 
basin-like character is preserved in this part of the valley by the succession of reen- 
trant angles in the northern escarpment. 



1 I'll'' headwaters of the Xahesna have iidI lici-n explored above the point where our route 

the rivi r 
•Twentieth Ann. Rent. CS.Geol. Survey, Pt.VJI.pp. 150 and 451. 



352 FEOM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

Where the Tanana leaves the mountains, near its head waters, the peaks on either 
side of the gorge rise over 4,000 feet above the river level. The summit of Mount 
Chisana, a part of the old plateau surface, is some 1,500 feet above the river, and the 
top of the escarpments which form the southern valley wall of the Middle Tanana 
are believed to have about the same amount of relief, though the elevations were 
unfortunately not determined and the contouring on the accompanying topographic 
map was made purely from estimated elevations. The ridges which bound the 
Tanana on the north near its mouth stand not over 300 or 400 feet above the water. 

The northern tributaries of the Tanana are all sluggish streams, flowing in broad 
valleys, and have considerable depth. They are as a rule clear or only slightly 
turbid, carry little sediment, and have no deltas at their mouths. The southern 
tributaries, having their sources in the high mountains, are all shallow, turbid, swift- 
flowing streams, usually with large deltas. The formation of these deltas is prob- 
ably the chief cause for the position of the Tanana River close to the north wall of 
its valley, though this may have been aided by warping. 

The Nabesna River is the mosi important tributary of the Upper Tanana and 
nearly equals it in size. Like the Tanana it leaves the mountains through a narrow 
Valley, and on reaching the lowland continues its course to the northeast until it 
joins the main river. The Tetling is a river of secondary importance, draining a 
group of small lakes which lie within the valley. These lakes probably owe their 
origin to the damming of the former course of the Tetling by the delta deposits of 
the Nabesna. Its old course is marked by a series of small lakes which may he seen 
on the topographic map. The Tok River is of comparatively small size and in its 
character is the exception among the rivers from the south. Rising as it docs 111 the 
depression between the Xut/.otin and Alaskan mountains, it is not fed to any extent 
by glacial streams or streams from the snow untains, and therefore has clear water. 

The Robertson and Johnson risers are both sw iftlv flowing, shallow, turhid streams, 

and the waters have a slightly greenish tinge. These rivers leave the mountains 
through narrow valley.-, and both have broad deltas and glacial sand bluffs at their 
mouths. The ( mod paster and Yolkmar rivers How in broad valleys and are sluggish 
st ica 1 1 is. The Vol k mar is said to have itssource in a rather rugged mountain region. 
The Delta River is much like the Robertson and Johnson in its general character, 
except that it- valley is somewhat broader. The Mahntzu and Silokrivers are simi- 
lar in character to the Helta, hut are considerably smaller. 

The Salehakct and Chena rivers were not visited by our party, hut both have 
broad, Hat valleys. The Nilkoka River and Baker Creek have the characteristics of 

the other rivers of the north side of the valley. The Cant well has turhid waters and 
many sand bars, hut in its long journey across the valley it has lost something of its 
swift character. The Toklal is a deep, muddy Stream, and in its lower course has a 

comparatively moderate current. It ha- never been explored, so of its upper course 

we have no information. 

From where the Tanana leaves the mountains until it reaches the north side of 
the broad valley at its first great bend it is a -hallow, swift-flowing stream, compar- 
able in every way to the White River. Below this point to the contraction of the 
valley, near where the Fortymile trail reaches it, the Tanana has a very slow current 
and a very tortuous course; in many places it consists of little but a chain of ox-how 
lakes. A few short riffles occur in this part of the river, hut usually the current does 
not exceed 2 or 3 miles in all. Below this sluggish part of the Tanana to a point 
about 10 milesabove the Cantwell River the current is usually very swift. Several 
rapids are marked on the map, none of which, however, are due to rock barriers. 
In the region of Bates Rapids the river lias spread out until it is several miles in 
width and has innumerable channels, sand liars, and islands. Below the Cantwell 
River to the mouth of the Tanana it is usually confined to one or two channels and 
has a current of from 3 to 5 miles an hour. 



brooks.] PHYSIOGKAl'HY. 853 

FORTYMILE KIVEK.' 

This river is tributary to the Yukon, which it joins in British North- 
west Territory about 30 miles above the international boundary. The 
drainage basin of Fortymile lies entirely within the Yukon Plateau, 
and its headwaters reach far southward close to the Xanana Valley. 
About 60 miles from its month the Fortymile forks, the southerly 
branch and its tributaries beading near the Tanana and tributaries of 
the White. The north fork has a general east-and-west course and 
heads opposite the Volkmar and Goodpaster rivers, which How into 
the Middle Tanana. The north fork has been but little explored, and 
its location on the accompanying maps is only approximate. It is said 
to flow through broad, shallow valleys. The basin of the south fork 
has been fairly well explored, and its creeks flow in broad, shallow 
valleys, the relief being from 800 to L,500 feet. Fortymile Creek 
itself has a well-marked bench some -too feet above the present water 
level, which Goodrich has shown to be an old valley floor. 8 Below 
this bench the river flows through a narrow canyon for much of its 
courses It leaves this canyon about 20 miles from the Yukon, and 
from there on has a broad valley. In this lower course it has but a 
sluggish current, while above swift water is frequent and rapids are 
not uncommon. 

The broad, shallow valleys at the headwaters of this stream are 
probably synchronous in origin with the old valley floor of the Lower 
Fortymile. While the basin lies entirely within the Yukon Plateau 
and the even upland surface is a very marked feature of the topog- 
raphy, yet a number of isolated mountains and mountain masses rise 
above the plateau surface. Examples of these are Fortymile Dome, 
Glacier Mountain, and Sixtymile Butte. 

PHYSIOGRAPHIC NOTES. 

In a previous report 3 I have attempted a brief summary of the 
physiographic development of the White River and Tanana River 
basins. The area now under discussion belongs to the same physio- 
graphic province, and hence the history of the development of its topo- 
graphic forms is similar. The investigations of the past season (1899) 
throw much Light on some of the problems, but as yet the notes have 
not been worked up in detail. In studying this area the physiographer 
is still hampered by the lack of sufficient topographic data and by the 
fact- that even where contoured maps are available the elevations given 

Rept. U. s. Geol. Survey, Pt. III. [886-1897, 



'See PI. XLIII. 
•Geology of the Yukon go!< 
p. 276. 
•Twentieth Ann. Rept. U.S.i 
•11 GEOL, PT 2 


1 district: Eighteenth Ai 
>eol. Survey, Pt. VII, pp. 

23 



354 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

are only approximate, they having been determined very largely by 
aneroid barometer. 

The Yukon Plateau, already described, is a peneplain which was 
formed probably in Middle Tertiary times. It slopes gently to the 
north and west, but has some undulations which have been ascribed to 
deformation. Unreduced areas or monadnocks rise above the pene- 
plain, in some eases to the height of 1,500 feet or more. The ranges 
lying to the south of the plateau are rugged, with sharp outlines, and 
are comparatively young topographic forms. Some broad gaps which 
are found in these ranges, such as Mentasta Pass and some depressions 
at the head of the Cant well, are believed to have been formed at the 
same time as the peneplain. Subsequent to the planation an oro- 
graphic movement took place and the area was elevated far above its 
present position, and during this cycle the rivers carved deep, broad 
valleys. A depression followed which brought the plain nearly to its 
present position, and the rivers began building up their flood plains. 
Another elevation revived the activity of the streams, and they incised 
their channels in their former Hood plains, whose remnants are now 
seen as terraces and bluffs. 

In the previous discussion of the development of the present drain- 
age m stem it was shown that the great gravel-tilled basin of the Mid- 
dle White and Tanana represents a part of an old river valley which 
Formerly drained eastward, and which was called the White-Tanana. 
It was also shown that the constricted portion of the Tanana Valley is 
a comparatively new cutting, ami that in this part of the river a divide 
existed between this lower pari of the Tanana and the river described 
above, which occupied parts of the Upper White and Tanana valleys. 
The Lower White, probably having its source in Ladue or Katrina 
rivers, was also a distinct river from the old White-Tanana. 

The work of the past season enabled me t<> trace the former water 
course of the White-Tanana eastward. It Leaves the .Middle White 
River Basin by the present valley of the Koidern (see Pi. XLVI, A 
and A'i. then, crossing the Donjek, finds its way by a broad, flat 
divide to Lake Kluane. From the eastern end of this lake the broad, 
flat valley of the Creadon River continues the old watercourse, proba- 
bly reaching Lake Dezadeash by way of the Schwack Valley. From 
Lake Dezadeash the old river turned aouthward across the flat divide 
which separates the lake from the Tatshenshini waters. From this point 
on I have no personal knowledge of this old waterway, but the best 
evidence available indicate- t hat it found its way to the sea by the Tat- 
shenshini 1 and Alsek valleys. The A.lsek is probably an antecedent 
river which maintained its position during the St. Elias uplift. 



1 In tl r discussion of tbis old drainage channel it was suggested that it might havi n 

Hi' ol Lynn Canal. The studies oi the past summer proved thai this supposition was 

m tin- divide between the ( hilkatand AJsek basins are too high in admit 
outlet. 





VIEW LOOKING NORTHWEST ACROSS THE DONJEK DOWN THE VALLEY OF THE KOIDERN RIVEF 
SHOWING LOW DIVIDE BETWEEN THE KOIDERN AND THE DONJEK 




I!. LOOKING ACROSS THE DONJEK, SHOWING CANYON ON THE RIGHT. 



BEOOJC8.] 



PHYSIOGRAPHY. 



155 



The basin of the Upper White during this time drained through a 
broad valley now occupied by a small stream and lake and running 
almost due eastward from the front of the Klutlan Glacier. Tins 
stream joined the main water course near the head of Koidern River. 
The accompanying sketch (fig. 21) shows the position of this old 
water course. The fact that the divides marking this old drainage 
system have small relief compared to the present waterways goes to 
-how that this change in drainage has been very recent. Our present 
facts do not warrant a definite statement as to the cause of this change 
in the river system. I would call attention, however, to the fact that 
a northwesterly tilting, corresponding to the present inclination of 




Fig. 21. — Sketch map showing former drainage channel. 

the plateau, would give the northward- and westward-flowing streams 
the advantage in rapidity of cutting, which would he quite sufficient 
to cause this change in drainage. The position of the ice front may 
have been the cause of the change. 'Where the Cordilleran Glacier 
reached its maximum extension the southward-flowing streams would 
he ice dammed, while the drainage to the north would he unimpeded. 
Among the striking features of the topography are the broad, Hat 
east-and-west valleys. The series of broad depressions which mark 
the old drainage channel of the Tanana-White have already been 
referred to. and there are several others running parallel to these. 

A.S examples we have the valleys of the Nisling, the Klotassin. and 
the East fork of the Kluane. A similar depression is said to connect 



356 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

the lower end of Aishihik Lake with the upper end of Lake Kluane. 
Another connects the valley of Kashaw River with Lake DezadeasH. 
In each case the size of the present stream is entirely disproportionate 
to the size of the valley. The drainage of many of these old valleys 
is taken by rivers flowing directly across them and leaving them by 
narrow canyons. The Upper White, the Donjek, and the river 
draining Lake Kluane flow northward across broad valleys and thence 
through narrow canyons. The broad depressions must be classed as 
consequent, the canyons as subsequent, drainage. PL XLVI, A, is a 
view looking westward across the Donjek and showing the consequent 
valley, which is parallel to the strike. PI. XLVI, />, shows the sub- 
sequent drainage through the canyon of the Donjek. 

The unadjusted drainage conditions are well illustrated by the 
Kashaw River. Shorty Creek, which is the name given to the upper 
part of this river, leaves the mountains through a narrow gorge and 
debouches on a broad alluvial fan in the Kashaw Valley. Though but a 
few miles from Lake Dezadeash, and separated from it by a very low 
divide, Kashaw River flows southward, away from the lake. It is stated 
on good authority that Shorty Creek sometimes Hows southward, 
sometimes northward, depending on what part of its alluvial fan it is 
occupying. An examination of the topographic map (PI. XLIII) will 
show that this diversity of drainage involves a circuit of a hundred 
miles or more. 

GEOLOGY. 1 

GNEISSIC SERIES. 

The oldest rocks of the region, so far as determined, are a complex 
of gneisses with various basic and acid intrusives. The gneisses, with 
which are associated crystalline schists, are intricately folded and 
often much sheared. In general, they are of an acid character, but 
basic schists are also present. The associated igneous rocks can !»• 
divided into two classes, namely, those that were intruded previous to 
the major deformation, which are much sheared, and the later intru- 
sives, which are comparatively massive. They include several varieties 
of granite with some dioritic and gabbroic rocks. if the relative 
amount of deformation be used as a criterion, the basic rocks are the 
older, the younger intrusives being of an acid character. The latest 
intrusive rock is a white granite, often aplitic, which is found massive 
in dikes throughout the series. 

The gneissic complex is well exposed on the Lower White, where it 
was studied by me in a previous season. The investigations of the past 
season (1891) ) have added but few facts relating to this group of rocks, 
for in the region north of the Tanana, where the main gneissic belt was 
crossed, there were very few exposures. A somewhat more detailed 



■See Pis. XLVII and XLVIII. 



TWENTY-FIRST ANNUAL REPORT PART II PL.XLVI 




BBOOKS.] OLDER SEDIMENTARY ROCKS. 357 

description <>!' the various rock types found with the gneisses is given 
in the reporl already cited. 

The gneisses arc classed as Archean because they are apparently older 
than all of the sedimentary rocks. The sedimentary series are believed 
to overlie the gneisses uncomformably. On the accompanying geolog- 
ical map (PI. XL VII) the gneissic series is shown to occupy a broad belt 
lying between the Yukon and the Tanana and extending eastward across 
the White. The extension of the gneisses east of the White is made 
on the liases of some notes furnished me by Dr. Hayes. 1 To the north 
the continuity of the gneisses is interrupted by two belts of the older 
sedimentary series, which are infolded with them. According to the 
best information these belts of sediments do not extend far to the west, 
and are so represented on the map. 

The general strike of the gneisses is northwest and southeast. The 
dip of the foliation is usually low and variable, though prevalently to 
the southeast. The series is entirely crystalline and includes no rocks, 
so far as known, of sedimentary origin. The cross jointing of the 
series has been previously described, 2 and the variation in direction of 
the jointing and its consequent effect on the topography has been 
ascribed to two synchronous thrusts coming from different directions. 

KOTLO SERIES. 1 

Mr. Spurr, in his account of the geology of the Yukon district, 
describes three series of sediments, which he names the Birch Creek, 
Fortymile, and Rampart series. He shows that the first two are con- 
formable and are overlain unconformably by the Rampart rocks. In 
my previous report on this region I describe two groups of rocks — 
the Nasina series and the Tanana schists. These were believed to be 
the equivalents of the rocks described by Spurr. but as no definite 
correlation could he made T was forced to use a new nomenclature. 
The western extension of the Tanana schists was recognized by Mr. 
W. C. Mendenhall, 1 and he applied tin' same name to them. 

On the accompanying map all these older sedimentary rocks have 
been grouped together under the name "Kotlo series." I have thus 
grouped together under this heading a number of different formations, 
probably including vast thicknesses of strata, but will make no attempt 
here to describe them in detail. For special descriptions see the 
reports already cited. 8 

I .mi much Indebted to Dr. Hayes n>r the use of his geological note's, made on the trip which 1ms 
i red tn. 

'Twentieth Ann. Rept. IT. S. Geol. Survey, Pt. VII, pp. 164 165, Bl-482. 

:i 0n the plate showing profiles and known geology (PI. XLVIII) these rocks are termed the Older 
Sedimentary series. 

1 a reconnaissance from Resurrection Bay to the Tanana River, Alaska, in 1898: Twentieth Ann. 
Rept. 0. S. Geol. Survey, I't. \ U,pp 266 340 

s In a recent publication Mr. R. Q. McConnell has described the rocks of the Klondike region and 
has grouped them In four differenl formations, having given to each a new name. These foi 
are probably equivalent to some of the rocksstudled by Spurr and myself in the Fortymile region, 
and would therefore be Included in the older sedimentary (Kotlo) series, See Prelimine 
on the Klondike gold fields: Geol. Surv. Canada, 1900, No. 687. 



358 FEOM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

This series is of especial interest, because it probably embraces all 
the gold-bearing rocks of the Upper Yukon. The rocks have only 
this one character in common, and are far from being a stratigraphic 
unit. The age of these older sediments has not been established. 
Mr. Spun - , in his studies of the Rampart rocks, believes them to be 
probably Silurian. The only paleontological evidence is a single 
shark's tooth. As far as known to the writer, no other fossil has ever 
been found in them. If the Rampart series are pre-Silurian, the 
Birch Creek. Fortymile. Nasina series, and Tanana schists are prob- 
ably lower Paleozoic or pre-Cambrian. 

These rocks have a general parallelism in strike to the gneisses, and 
their dips arc \ cry variable. In general the. dips are low, the type 
structure being an open fold. The rocks of the older series in 
this subdivision are considerably metamorphosed, being often quite 
crystalline. The lowest beds of this group are quartz-schists, fre- 
quently containing sonic clastic crystalline material (Birch Creek 
series and Tanana schists). These quartz-schists become calcareous 
upward and are succeeded byavasi thickness of limestone, which is 
usually crystalline (Fortymile series. Xasina series). Above the lime- 
stone- an unconformity occurs, and above this effusive rocks of vast 
thickness are found (Rampart series). The beds below this uncon- 
formity -liow evidence of having suffered much more deformation 
than those above. Throughoul the older sediments acid and basic 
intrusive- are not uncommon. 

GREENSTONE-SCHISTS. 

The greenstone-schists Bhown on the geological map in the White 
and Tanana River valleys are chiefly of a gabbroic and dioritic char- 
acter, with numerous schists made up largely of secondary minerals, 
such as chlorites, actinolite, zoisite, and epidote. Among them are 
some finely banded rocks which, when studied under the microscope, 
were found to be tuffaceous. The investigations of 1898 showed these 
rocks to be largely intrusive and to lie younger than the Tanana schists, 
which are here included in the Kotlo series. 1 These rocks are differ- 
entiated from the gabbroic and dioritic rocks, to be described below. 
because they are far more schistose. These greenstone-schists seem 
to be more closely related to those found associated with the gneisses 
than to any other intrusives of tin' region. They were in a previous 
report correlated with Spurr's Rampart series, but this correlation, on 
further study, seems doubtful, and the}' are therefore mapped as a 
distinct series. 



in the White and na riverbasins: Twentieth Ann. Kept. U. S Geol.Survey, 



YOUNGER SEDIMENTARY ROCKS. 359 



NUTZOTIN SERIES. 1 

Along our route of travel from Pyramid Harbor to the Nabesna 
River were exposed slates, white limestones, and flags, with some sand- 
stones. These rocks are rather closely folded and strike in a north- 
wot -southeast direction. From the general facts of their distri- 
bution and the relative amount of deformation it is believed that they 
are younger and that they overlie the older sediments uneonformably. 
Future work will undoubtedly resolve the rocks of this series into 
many different horizons, but for the present purpose it has been 
thought best to group them together. Professors Reid and Gushing 
in their work around Glacier Bay 2 found a series of wmite limestones 
and argillites. In the former they found fossils of Carboniferous age. 
These locks of Glacier Bay have been included with the younger sedi- 
ments, both on lithological similarity and paleontologieal evidence. . 

In the upper basin of the White River, on Kletsan Creek, are expo- 
sures of a white limestone which carries many fossils. Many of the 
fossils collected from this point were unfortunately lost, but a few 
which were submitted to Mr. Charles Schuchert, of the United States 
National Museum were determined to be of Carboniferous age. 1 
make the following extract from Mr. Schuchert's report on these fossils: 

Kletsan Creek ("9 AJB171"): 

Productua cora ) 

Productus, 2 undet. species.) 
Seminula, 1 undet. species. 
.v. nopora, 1 undet. species .] 
Pebble from Kletsan Creek ( "VI AP. 150"): 

Fusuiina (not the common American species, F. cylindrica). 
These two localities are of one general horizon in the Upper Carboniferous, which 
-ecu i to lie the same zone as that near Circle City discovered by Mr. Spurr (Takandit 
series) or a closely related one. [ have made no specific determinations, since 
the fauna is not to he correlated w ith that of the Upper Carboniferous of the Missis- 
sippi Valley, hut with the Fusuiina zone of China, India, and the eastern slopes of 
the Qrals. ' 



White crystalline limestone. 



This belt of limestone was traced from near the Kashaw River to 
the Nabesna with more or less interruption. Immediately underlying 
the white limestone are series of slates or argillites, possibly the same 
as those on Glacier Bay. already referred to. 

In the report cited I have described what I have called the Wellesley 
formation, which consists of heavy conglomerate beds associated with 
black slates. The few fossils which were collected from these slates 
show that the formation IS of either Devonian or Carboniferous age. 
and this area, therefore, is included with the younger sedimentary 
series. 

1 On the plate showing profiles and known geology (PI. XLVIII) these rocks are termed the Younger 
Sedimentary series. 
8 See footnote 9 on p. 341. 



360 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

On the above rather fragmentary evidence a belt of rocks running- 
parallel to the St. Elias Range at its northern margin has been indi- 
cated on the accompanying map and provisionally named the Nutzotin 
series. This belt is interrupted by the younger effusive rocks and by 
the Pleistocene deposits of the larger valleys. 

Like that of the rocks of the region, the strike of this series is about 
northwest and southeast. The dips are variable, but more often to 
the south than to the north. The type of structure is rather of closed 
folds, sometimes plainly overturned to the north. The deformation 
resembles the Appalachian structure and differs very materially from 
the open-fold type of the older rocks lying to the north. 

If the interpretation is correct, the oldest bed of this series is the 
heavy conglomerate, included in a previous report in the Wellesley 
formation, on the Upper White and Tanana. This is succeeded by 
black slates, often much crumpled, and becoming more calcareous 
toward the top. Then there is a great thickness of slates, graywackes, 
and impure limestones, in ascending order, intruded by many basic 
dikes and containing probably some effusive igneous rocks and tuffs. 

This pari «>f the series was well exposed on the Nabesna River, along 
our route of travel, it here contains much igneous material and some- 
what resembles Spurr's Rampart series of the Fortymile basin, but 
for structural reasons, as well as because of its area] distribution, it 
is correlated with the younger clastic series the Nutzotin series. 
Deposits believed to lie the equivalent of these beds, exposed on the 
Nabesna and Lynn Canal, contain little, if any. igneous material. The 
youngest beds of the series i> the limestone, usually crystalline, in 
which, as has been stated, fossils have been found. 

When the region is studied in detail this series will undoubtedly 
receive many subdivisions, tor as mapped it must include beds aggre- 
gating many thousand feet in thickness. It is quite probable, also, that 
in this hasty reconnaissance some older beds have been included in this 
younger series. 

Atseveral Localities igneous rocks which are plainly effusive rocks 
were found associated with this series. These effusives are quite dis- 
tinct from those regarded as Tertiary and Pleistocene and are probably 
much older. No areas of these older effusives were found large enough 
to represent on the accompanying geological map. With them were 
found some tuffs and conglomerates, the pebbles of the latter being- 
made up of effusive material. Such rocks were noted along the south- 
ern margin of Lake Kluane. 

INTRUSIVES. 

The intrusive rocks of the region have been differentiated into two 
i-lasses on the accompanying map — those of a granitic type and those 
of dioritic and gabbroic types. The former are by far the most 



INTBU8IVE ROCKS. 361 

extensive. The largest area of granite is that of the Coast Range, 
which has been traced by Dr. Dawson. Dr. Hayes, and others from 
British Columbia to the Chilkoot Pass. Typically this is a hornblende- 
or biotite-granite, usually more or less uniform. 1 found a granite 

of this character near Rainy Hollow and again near the eastern end of 
Lake Kluane; also on the Nabesna. Near the Kluane Valley Dr. 
Hayes crossed a similar belt of granite, which is represented on the 
accompanying map. Granite has also been reported both southeast 
and northwest of Dezadeash. The distribution of these areas suggests 
that they all belong to the same intrusive mass, which was injected 
alony an axis running northwest and southeast. It is quite possible 
that future work will trace a continuous bod}* - of granite throughout 
this belt. In the work of the past summer the granite was found to 
be massive, but to have well-developed joint planes. 

In studying the section from Skagvvay across the White Pass shear 
zones were found in the granite, along which it had been altered to a 
finely foliated schist. These shear zones are of very small extent and 
are probably lines of faulting. At Skagway and at other points along 
this route the granite is found to be cut by dikes of di'oritic and 
diabasic character. About 5 miles west of Skagway a large mass of 
porphyritic rocks was observed, which is probably effusive. The talus 
slopes and stream gravels at other points along this route indicate that 
there are other considerable masses of effusive rocks at various locali- 
ties within the area of the Coast Range granite. At the upper end of 
Lake Kluane dioritic and diabasic dikes were found cutting the gran- 
ite, and also syenitic rocks. Coarse pegmatites have there also an 
extensive development. On the Middle and Lower Tanana hornblende- 
granites of a similar type were found associated with the gneisses and 
mica-schists, which are classed as Archcan. These granites lie on the 
extension of the same axis of intrusion. Similar areas of granite 
entirely distinct from those on this axis were found in various parts 
of the region, but most of them are too small to show on the accom- 
panying map. One mass is represented at the big bend of the Lower 
White. My investigations lead to the conclusion that this granite is 
post-( Jarbonif erous and pre-Cretaceous, and Dr. Dawson has determined 
that it is post-Triassic in age. 1 

Of the more basic intrusions of the region little can be definitely 
stated. In the locks of both the lower and the upper sedimentary series 
dikes which should be classed with this group are found. The green 
stone schists of the I'pper Tanana and White have already been classed 
with similar schists which occur in the gneisses. T1k> rocks here indi- 
cated as dioritic and gabbroic intrusives, probably including diabasic 
and other basic rocks, are almost entirely massive, and are a distinct 

i Yukon ilistrict and British Columbia: Qeol. Surv. Canada, Vol. Ill, 1887 88, PL I, p. 82 B. 



362 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

series in these greenstone schists. Professors Cushing and Reid have 
mapped as diorites and quartz-diorites rocks of this character occur- 
ring on Glacier Bay. Along the Upper Tatshenshini I found some 
pyroxene-feldspar rocks which are put in this group. The innumer- 
able dikes of this character found in some parts of the Nutzotin series 
have already been described. While this grouping together of rocks 
of such varied character is unsatisfactory, vet it is all that our present 
knowledge warrants. 

TERTIARY ROCKS. 

TOK SANDSTONE. 

A small area of this rock was described and mapped in 1898, and I 
quote as follows from my report: 

A few miles below the mouth of theTok River several exposures of a soft, yellow 
sandstone were found. This sandstone, though of small area! distribution, lias been 
given a special name because it is probably younger than any of the formations 
alreadj described. It has a yellowish color, is friable, and is thin bedded. Beds 
of fine Eeldspathic conglomerate of no great thickness arc found in it. The sandstone 
itself showed a thickness of somewhat over 50 feet at one locality. 

Several basic dikes of considerable size were found cutting the sandstone at rfght 
angles to the bedding, and these were usually deeply weathered. A microscopic 
examination of one of the dikes showed it to be an olivine-diabase. The strike of 
these beds is about E. and \\\, and the dip, \\ hich is rolling, uot over5° or 10°. This 
strike is entirely at variance w ith that of the gneisses w hich are near at hand. 

Fragmental plant remains were found in the Tok sandstone, hut. unfortunately 

arc not well enough preserved to give any clue as to the age of the beds. From their 
slight deformation and unaltered appearance I am inclined to regard them as post- 
Paleozoic and most likely of Tertiary age. 1 

While we were in the valley of the Caskawulsh River we could see 
far to the south of us high escarpments of bedded rocks (lipping 
southward, forming the front of the Si. Klias Range. Interheddcd 
with them were masses of dark intrusives, which in places could be 
seen to cut the bedding. This series was seen to overlie some older 
rocks unconformably. No opportunity was afforded to study this 
series, except from a distance, hut it seems probable that they are of 
Tertiary age. 

TERTIARY EKFUSIVES. 

On the accompanying geological map large areas of effusives ate 

marked as occupying the northern margin of the St. Elias Range. 
These rocks include rhyolitic, andesitic. dacitic, and basaltic types, 
but no detailed study has been made of them. Volcanic tuffs are also 
not uncommon, and some fragments of volcanic glass were found. 
The age of this series is not definitely determined. They are inti- 

i Twentieth Ann. Kept. U. S. Geol. Survey, Pt. VII, p. 173. 



brooks.] TERTIARY AND PLEISTOCENE DEPOSITS. 363 

mately associated with volcanic rocks which have been bul recently 

ejected, and which must be considered as of Pleistocene age. The 
larger masses, however, show evidence of being older and have been 
more or less deformed. This deformation manifests itself in mono- 
clinaJ uplifts which dip south and present fault escarpments to the 
north. Along these escarpments evidences of crushing and shearing 
were found wherever opportunity was offered to study them. Along 
the route of travel between the Kaskawulsh and Nabesna rivers, at 
different points, we saw innumerable escarpments of this series, but 
opportunity was given for studying only the ones lying adjacent to 
our course. In general, it can be stated that where these effusive 
rocks occur along the northern margin of the St. Elias Range they 
appear in these faulted blocks. The type of structure is similar to that 
described by Russell along the southern margin of the range, near 
Yakutat Bay, where the fault blocks dip northward. 

As our best evidence goes to show that no d} r namic disturbances of 
this character have occurred since Tertiary times these effusive rocks 
are regarded as of Tertiary age. In a broad depression which con- 
nects the Upper White with the Upper Tanana there are a great num- 
ber of mesas made up of volcanic material and usually capped by some 
hard rock. These effusive rocks exhibit a slight tilting to the south. 

On the headwaters of the Tatshenshini River some effusive rocks were 
found which have been grouped with the others on the accompanying 
map. They show relatively the same amount of deformation, but in 
the hand specimen have the appearance of rocks considerably older. 
They can be conveniently grouped under the held term ki felsites.' , 
With them arc tuffs and conglomerates containing fragments of the 
Coast Range granite, showing them to be of younger age and sepa- 
rated by an erosion interval. At various localities in this region rocks 
of similar type have been found, but these have not been studied in 
detail. In a previous report the mention has been made of some 
andesitic rocks on the Lower White, and also on the Middle Tanana in 
the vicinity of Tok River. From their general appearance these 
rocks should be grouped with those of the Upper Tatshenshini, and 
probably represent the oldest outbursts of Tertiary times. 



PLEISTOCENE DEPOSITS. 
SEDIMENTS. 

On the accompanying map (PI. XLYII) the water-laid Pleistocene 
deposits are represented. The limit of glaciation is shown, but no 
attempt has been made to map the purely glacial deposits, as the 
region has not been studied in sufficient detail. The Pleistocene beds 
are, for the most part, old river gravels, lacustrine silts and sands. 



364 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

together with the moraine river gravels and silts. The old river 
gravels have the same history and the same origin as those which are 
at present being laid down. In some cases the slight elevation has 
resulted in a new river channel being incised in the old deposits, thus 
giving the silt and gravel terraces which are so common in some parts 
of the region. In other cases these old gravels are distributed along 
valleys which, by the change of drainage, are now abandoned, the 
drainage having sought new water courses. In the study of both the 
older Pleistocene deposits and (hose which are now being laid down 
in the lakes and rivers, it has been found impossible to differentiate 
the fluvial from the lacustrine deposits. Such differentiation, in my 
opinion, can be made only from topographic and physiographic evi- 
dence. 

1:111 v|\ ES. 

The effusive rocks of the region have already been described and 
the probable Tertiary age of some of them has been considered. Some 
of these effusives undoubtedly belong with the Pleistocene deposits, as 
the\ are of very recent ejection. No attempt has been made on the 
accompanying map to differentiate the Pleistocene and Tertiary vol- 
canics. Effusive rocks of recent age have been described from various 
partsof Alaskaand are probably synchronous outpourings. Examples 
of these are the volcanics of the Wrangell group, 1 the basalt Hows of 
White-Horse Rapids and Fort Selkirk, ami the volcanic rocks of the 
Alaskan Peninsula, Aleutian Islands, and Lower Yukon. 

GLACIAL PHENOMENA. 

The glacial phenomena of the region can be differentiated into that 
of the present glaciers and that of the Cordilleran ice sheet, On our 
trip from Lynn Canal to the Nahesna River we saw innumerable 
glaciers which had their source in this snow range and the White 
River route. A few of these are shown on the accompanying map, 
but many it is impossible to locate (see Pis. XLI. J, and XLV, A). 
Among the larger glaciers which we passed were the O'Connor, the 
Donjek, the Klutlan, and theTanana. These all occupy valleys of con- 
siderable size. In every instance studied by the writer the glaciers 
were found to be retreating. A few small glaciers were also seen in 
the Nutzotin Mountains, to the north of our route of travel. These 
are of interest because they are probably the most northerly glaciers 
thus far found in Alaska. 

The limit 2 of glaciation on the accompanying map shows three long 
tongues extending down the \ alleys of the Nabesna, Tanana, and White 

'Mr. Rohn kindly furnished some information in regard to the region between the Chitina and 
the Upper Tanana. 

- East of White Hirer this limit of glaciation 1- determined by the work of Dr. Hayes, Dr. Dawson, 
Professor Russell, and Mr. .1. B. Tyrrell, in n-[,,,rts already cited. 



brooks.] VOLCANIC DEPOSITS. 3(>5 

rivers. Of these, the Nabesna and White River tongues were deter- 
mined by field observations; the Tanana tongue only by inference. 
They simply represent a valley glacier which extended beyond the ice 
front at the time of maximum glaciation In the case of these valley 
glaciers the sides of the valleys are found to be glaciated only up to n 
certain limit, which gradually decreases in elevation to the northward. 
At the end of the valley glacier of the Nabesna River a morainic topog- 
raphy was observed. 

Lt seems quite probable that there was no connection between the 
glaciation of the Alaskan Range and that of the St. Elias Range. 
From the best reports we have, the region between the Upper Copper 
and the Upper Tanana is not glaciated, and hence the Alaskan Range 
probably represented a different center, from which the ice radiated 
in all directions. Whether this glaciation in the Alaskan Range was 
synchronous with that of the St. Elias must be determined by i'utur • 
investigation. In the glaciated region the deposits are not plentiful; 
only a few exposures of till have been observed. Glacial erratics are, 
however, very common. At a number of localities glacial moraines 
were observed, but these belong very largely, if not entirely, to the 
present epoch of glaciation. On the accompanying geological maps 
no attempt has been made to differentiate the glacial from the other 
Pleistocene sediments. 

VOLCANIC TUFF. 

The white volcanic ash which is found on the Pelly, Lewes, and the 
Upper White has been noted by many writers, and has been especially 
studied by Dr. Dawson and Dr. Ha} 7 es. In a previous publication I 
have added some notes to Dr. Hayes's accounts of its distribution. 
The work of the past summer has yielded considerable information in 
regard to this interesting deposit, but it is not within the province of 
this paper to discuss it. In a westerly direction the volcanic ash has 
been traced far beyond what was formerly supposed to be its limits, 
ll occurs as far west as the Forty-mile Basin and east to the O'Connor 
Glacier. Near the margin of the area it is found simply as a thin film 
immediately underneath the soil, and can be observed only when the 
conditions are favorable. In thickness this deposit varies greatly. 
On the Upper White, as described by Dr. Hayes and observed by the 
writer, large drifts 100 feet deep were seen, while near the margin 
of the region the thickness of the lied is hardly measurable. That this 
is a wind-laid deposit' is clearly shown by its distribution. It occurs 
on mountain tops and on valley slopes, as well as along river bottoms. 

1 Prolessor Hellpnn a theory that this ash is a lake deposit becomes utterly untenable when the 
facta <>i Its distribution are studied. II seems doubtful whether Professor Beilprin had read Dr. 
Hayes's paper, for die facts presented in it arc sufficient to confute the theorj of it* being a 
lacustrine deposit. See Alaska and the Klondike, pp. 228-288. 



366 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

Along the valley of the Upper White River it is distributed as huge 
drifts, which from a distance closely resemble snowdrifts. 

The location of the volcano from which these ejecta came is not yet 
determined. From the distribution of the ash and the relative coarse- 
ness of the material at different localities the writer is inclined to 
believe that the volcano lies to the south of the Klutlan Glacier, well 
in the heart of the range. The Klutlan Glacier, besides carrying 
much ash, also brings down considerable white pumice, the fragments 
being sometimes 6 inches in diameter. These are probably a part of 
the same ejecta as the ash. Of the glaciers and streams the Donjek 
and the Klutlan must have their sources nearest the volcano. 

It is of interest to note that at several localities two layers of ash 
were observed, separated by several inches of soil. This fact suggests 
that there were two outbursts separated by a considerable time period. 
In favorable localities the soil was able to gain a foothold before the 
second outburst. At the Klutlan Glacier some pebbles of a white vol- 
canic rock were found, which may represent lavas of the same period 
of activity. 

GROUND ICE. 

The ground-ice formation of Alaska has been frequently described 
and needs no further description here. Below the immediate vegeta- 
tion of the surface the ground is, as a rule, fro/en throughout the year. 
Thawing takes place only along fresh stream cuttings or where the 
moss or grass has Ween stripped oil'. In some cases this ground ice is 
clear, resembling glacial ice, but in origin it differs little from that of 
the frozen soil. These clear ice masses represent small lakes which 
have congealed. 

The dense growth of moss, which covers nearly the entire surface of 
the country, retards erosive action very materially. Streams are usu- 
ally clear, even after rainfall, unless they have glacial origin or are 
undercutting silt banks. Where rocks are exposed among the higher 
peaks as cliffs, disintegration takes place very rapidly, probably because 
of the extremes of temperature. 



TABLE OF coKKELATION. 



367 



jf 




. 




































57fi 

81 


&> 




| 1 






| 




f|i 


"5 

5 




! 1 






5 










t 13 










* 


S 










* 






















- J "= r' 
















■c . 


S-H 5 J 


= 5 










5 p 


^ 


C J 




«'l 




>j 






°S 


| 


II 


.. _o = — 
















'3 -J 


5o3 oq § . - 

: - = S $ 













gbg 


2 


2 M 


w 






M 






o 


-7. 


« 


_ 




71 • 




.*': ?' 




- 3 






II 


bo 
~ 

h 


^ 
^ 




,2M§ 

III 




JO 

so 

^£ i 






s 


1st 


a 


•Eli 

o s a 










X 


DO 


H 


•" 


H 




5 H 






•J. >.* 


| 






i 






i 




««a-. 


c 






o 




„; 


H -i 




I^i 


s 






08 




'C 


II 




liSI 








d 
a 




J 


n 2 




- 


/. 






3 




02 


s ~ 




~_ ', 














m - 


































S3 


■§2 

7 jja 

§§i 

1 = 5 




.. z. '■'. 


si 


3 








"■d 


1 


p 2.- 


d 


1 








2 J4 


af^-l 


1 




J 










95 


g£^ 


d 


s 


3j 


s 








* 


o 


c 


t,£ 


gJ* 


■c c 










«- 




| s 


&2 


= ;/. 








a 


i. 




h"s 


a -a 


£ ° 








i 


,o 


■c 
















c 3 
o w 

h 


c 


« 


T - 


H 


— ' 






a 





o 






5? ji 


a 






Ss 






13 
d - . 




- = 7 - 
lei's 

o : - s - 
> a. ^ fti £ 


= 


6 






g I 3 

ill 


I 
1 


~ 


K 


H 


M 


53 




H 


- 


pq 


















£ 


i-~ax 






















•-' 


&«- -',- 








| 




; 






1 


! 


•a . 


j!fsg 

lllil 

pass 


c 

r 






5 




^ 






u 




a 


X 


< 





.5 5= >.i 



^1 |k 

I J fill 

Kill 



f c~^ • 






^25i-53 
ts * S g 3 *> 



- / / /. y! / 

^- C d c c c 
£; a c e d d 

V iOOOC 



368 FROM PYEAMID HARBOE TO EAGLE CITY, ALASKA. 

SUMMARY OF GEOLOGY. 1 

A broad belt of crystalline rocks extends in a northeast-southwest 
direction in the region of the Tanana- Yukon divide, embracing a series 
of gneisses, niiea-schists, basic schists, and various intrusives, chiefly 
of an acid character. Near the Middle Tanana this series bends to the 
west and south, and its continuation is to be sought for in the region 
of the Upper Kuskokwim. 3 To the southeast this belt is probably con- 
tinued by the granitic rocks on the Pelly River, described by Dawson. 
What evidence we have goes to show that this is the basal series of the 
Yukon Basin, and as it contains no recognizable detrital material it can 
properly be assigned to the Archean. Whatever the original charac- 
ter of the rocks may have been, they are now essentially mica-schists 
and gneisses, with considerable intrusive material. The gneisses and 
schists, and in part the intrusives. have been subjected to intense dy- 
namic metamorphism. Their metamorphic condition is the strongest 
argument, for considering them older than any of the sedimentary 
rocks. The intrusives are both sheared and massive and hence were 
injected both during and after the period of folding. 

After the era of the folding of the gneisses the next important 
epoch in the region is that during which the older sediments, the 
Kotlo series, as marked on the accompanying map, were deposited. 
The oldest rocks of tins series contain more or less detrital crystalline 
material, and it is probable therefore that during this epoch a pail of 
the Archean area was exposed as a land mass, and was, in part at 
least, the source of the sediments. The oldest rocks of the series are 
present, — quartz-schists with impure limestones, called the Birch Creek 
series by Spurr (Tanana schists. Brooks). This series aggregates 
many thousand feet in thickness. This period was followed by the 
deposition of an immense thickness or limestone beds. :t 

Acid and basic rocks are found in both the arenaceous and calcare- 
ous beds. The close of the deposition of this calcareous series was 
marked by dynamic disturbances, and these beds were folded, and 
probably during this time the intrusion of the igneous locks took 
place.* After the dynamic forces had become quiescent once more, 
these older series, in part, formed land masses, which contributed 
sediments. A stratigraphical break is here marked l>\ the uncon- 
formity below the Rampart 5 series and greenstone-schists, which con- 
stitute the upper member of the Kotlo series. This epoch was char- 
acterized by the extrusion and intrusion of a vast amount of igneous 

i See Pis. XLVII and XLV 1 1 1 . 

'Spurr's crystalline rocks of the Kaiyuh Mountains, which he regards as basal, seems to bea dis- 
tinct belt lying to the northwest of the one under consideration: Twentieth Ann. Rept. 0. 8. Geol. 
Survey, Pt. VII, p. 211. 

3 Fortymile .series, Spurr, and Nasina series, Brooks. 

■•Geology of the Yukon gold district, pp. 255-256. 

& Spurr, op. cit. The greenstone-schists have been provisionally correlated with the Rampart series. 



brooks.] STMMARY OF GEOLOGY. 369 

rocks, chiefly of a basic character. This upper member of the Kotlo 
series is believed to belong to the lower Paleozoic. To the east of the 
areas mapped the Kotlo series has not been recognized, while to the 
west Spun has identified them in the Birch and My nook Creek basins. 
The series is of the utmost importance because the gold of the Yukon 
district, so far as determined, has been derived from the mineralized 
zones found in it. 

The Nutzotin series is the next succeeding formation marked on the 
accompanying geological map. This series is of Devonian and Car- 
boniferous age, and, as determined in the Fortymile 1 and upper Tanana 
basins, overlies the Kotlo series unconformable This unconformity 
was rather one of erosion than of deformation. The older rocks were 
in part above water and contributed sediments while this series were 
being deposited. 

I have described the heavy conglomerate of the Wellesley forma- 
tion in the upper Tanana and White River region, 2 which there rep- 
resents the basal member of the Nutzotin series. These are succeeded 
by black slates, which are overlain b} T impure limestones. Above these 
is a considerable thickness of gray and greenish slates and graywackes, 
growing more calcareous upward, and with them is a great quantity of 
basic intrusives, together with tuff's and extrusive rocks. These igne- 
ous rocks can be conveniently grouped together under the field term 
greenstones until they have received careful microscopical determina- 
tion. The uppermost member of this series is a bed of limestone 
probably exceeding a thousand feet in thickness, which is usually 
highly crystalline. This slate, limestone, and greenstone series was 
traced eastward along our route of travel to Lynn Canal. Reid and 
Gushing have described the sedimentary rocks of the Muir Glacier 
region as argillites and limestones, and these have been provisionally 
con-elated with the Nutzotin series on the accompanying map. Tbe 
rocks lying adjacent to the Coast Range along the Lewes River route, 
as determined from descriptions by Dr. Dawson and from personal 
observations by myself, undoubtedly belong to the same series, and 
have been so colored on the accompanying map. 

Fossils have been found in this series at several localities, so that 
its position in the stratigraphical column is approximately determined. 
On the Yukon Spurr 3 has found an upper Carboniferous fauna. On 
the Tanana* fossil evidence goes to show that this series is Devonian 
or Carboniferous. The Glacier Bay 8 limestones have been proved to 

ISpurr's Tuhkandit scrips is included in the Nutzotin series. For the distribution nnd relation of 
the Tahkandil series see Spurr's report. 

' I ip eU.,pp. 170-472. 

■'Op. ,it.. p. no. 

1 A r mnaissance in the White and Tanana river basins: Twentieth Ann. Kept. I". S. Qeol. Survey, 

Pt. VII, p. 172. 

'■■■i' icrBay and Its glaciers, by Harry Fielding Reid: Sia nth Van. Rept. I . S. Geol.Survey, 

Pt, i. pp. i.;: i ;i. 

21 GEOL, PT 2 24 



370 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

be of ■ Carboniferous age. Dr. Dawson 1 has found Carboniferous fos- 
sils in the limestones of Tagish Lake north of the Coast Range. These 
facts show that the Nutzotin series is largely Devonian and Carbonif- 
erous, but as represented on the accompanying map it may include 
older beds. 

No Cretaceous rocks are represented on the geological map, though 
it is quite possible that they may be found on more detailed examina- 
tions.' 2 Dr. Dawson has determined some areas of Cretaceous along 
the Lewes River, notably on Lake Lebarge. Spurr's Mission Creek 
scries of the Yukon district is believed to be of O'etaceous age. 
These Cretaceous rocks, as shown by these writers, are thrown into 
open folds. 

Intrusives are common throughout the series which have been so far 
described. They can be classed as rocks of granitic, dioritic, gab- 
broic, and diabasic character. The largest mass of intrusive rock is 
represented by the Coast Range granite. This is a medium-grained 
hornblende- and biotite-granite of a rather uniform character. At 
Lynn Canal this belt is about 60 miles wide. To the northwest a 
similar granite was found near Lake Kluane and on the Nabesna. 
It seems probable thai the belt is continuous, though it has not been 
traced by field observations. To the southeast Dr. Dawson has traced 
(his granite as Ear as the Stikine River. The investigations of the 
writer lead him to believe that the granite is post-Carboniferous and 
pre-Cretaceous. Dr. Dawson has determined that it is post-Triassic 
in age. In the section across the White and Chilkoot passes some 
shear zones are observed in the granite, along which it has been 
altered to a mica-schist. This goes to show that some dynamic dis- 
turbances have taken place since the intrusion of the granite. 

A second class <>!' intrusives, which are shown on the accompanying 
map, are classed as dioritic and gabbroic in character. The only 
large area of this type shown is that of the region of Muir Glacier, 
which is taken from Professor Reid's geologic map. These rocks are 
believed to lie younger than the granite, in which are found dikes of 
the same character. 

Of Tertiary sediments we have only one small area in the region. 
This is the so-called Tok sandstone, found near the mouth of the Tok 
River, the beds of which are gently undulated. 

The large belts of effusive rocks shown on the geological map are 
probably but the scalloped margins of much larger areas occurring to 
the south. This is shown by the abundant volcanic material brought 
down by the streams and glaciers which have their sources in the 
mountains of that region. In the Wrangell region we have more 

' Exploration in Yukon district, Northwest Territory, and in BritMi Columbia, p. 33 B. 
-Jurassic fossils were found by Hayes south of theSkolai Paaa (op.cit., p. 140), and beds which were 
probably Jurassic are reported by Robn from the Wrangell region. 
3 Op. cit., p. 32 b. 



bbooks.] SUMMARY OF GEOLOGY. 371 

definite information of the occurrence of large masses of effusive 
material. 1 

No study has boon made of the various effusive rocks which were 
collected by me, but a hasty examination showed rhyolitic. andesitic, 
dacitic, and basaltic types. Tutfaeeous rocks are very common, and 
some fragments of volcanic glass were found near the Klutlan Glacier. 

No attempt has been made on the accompanying- map to differentiate 
the volcanics of different epochs. In general it can be stated that the 
outburst began in late Tertiary times and probably reached its maxi- 
mum development in comparatively recent times. Some of the vol- 
canoes of the Wrangell group are still smoking, but it is not known 
whether or not this is simply a temporary quiescence or the solfataric 
stage which precedes the complete cessation of activity. To the north 
of the region mapped small areas of recentlv extruded rocks are not 
uncommon. As examples, we have the basalt of White Horse Rapids, 
at Fort Selkirk, and at various other points on the Yukon. One of 
the manifestations of recent volcanic activity is the white volcanic ash 
whose wide distribution has already been referred to. 

The volcanic rocks of the northern margin of the St. Elias Range 
and of the upper White River show evidence of having suffered some 
disturbance. To the south of our route of travel, between the Donjek 
and the White, we could see a number of northward-facing escarp- 
ments, the nearest of which was determined by actual observations to 
be made up of volcanic rocks; the others, lying to the south, were of 
a similar character, so far as could be determined by examination 
with held glasses. The tops of these escarpments are moss and grass 
covered and slope gently southward in conformity with the bedding of 
the constituent rocks. At several points the most northerly escarp- 
ment was examined and the rocks were found to be much sheared and 
shattered. This evidence goes to show that faulting has taken place 
along the escarpments, and that, in fact, these are monoclinal blocks 
tilted to the south and faulted on the north side. In the broad 
depression which connects the upper White with the upper Tanana 
there are a great number of mesas formed of volcanic material and 
usually capped by some hard bed. In these the strata also show a 
tilting to the south. 

The history of the unconsolidated Pleistocene deposits has been 
referred to in the physiographic notes, and has been somewhat more 
fully discussed in a previous publication. At only one locality in this 
region was there any evidence of the deformation of the unconsolidated 
beds, such as has been noted elsewhere in Alaska. In the mud Hats at 
the mouth of the Slims River at the head of Lake Kluane. some silt 
beds were observed which rise above the general Level of the Hood plain 

1 Messrs. Hayes, Allen, and Holm. 



372 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

in a series of little hummocks. On examination the material was 
found to be a finely banded blue clay which had been thrown up into 
a series of gentle folds. This folding may have been produced by 
some local cause- and not by a deformation due to dynamic forces. 
In general, during Pleistocene times the dynamic disturbances have 
been orographic elevations and depressions rather than deformations. 

The geological history of the important orographic features of the 
region has already been referred to, but a brief summary is necessary 
for the sake of emphasizing certain leading features. The Yukon 
Plateau is a dissected upland plain lying between two great mountain 
systems. On the north it is bounded by the Rocky .Mountain chain 
which lies between the Mackenzie and Yukon basins. This chain has a 
northwesterly trend nearly to the Arctic Ocean, then makes an abrupt 
turn to the west and continues parallel to the frozen sea. Its westward 
extension, which decreases very much in elevation, probably reaches 
the sea in the vicinity of (ape Lisburne. This part of the Rocky 
Mountain chain i- practically unexplored. 1 It is, however, known 
that the Paleozoic column is represented in northern Alaska 1 as well 
as the ( Yetaceous, and there is at Leasl no evidence against a correlation 
of this northern range with the Rocky Mountains. 

To the south the Yukon Plateau is limited by several distinct ranges. 
The most westerly of these is the great Alaskan Range, which lies 
wesl "f Cook Inlet and the Sushitna Valley and extends in a northeast 
direction to the Tanana. This range, so far as known, is largely 
made up of metamorphic schists, which should probably be included 
in the older sedimentary series of the accompanying map. To the 
east of the Alaskan Range the boundary of the plateau is continued 
by the Mentasta and Nutzotin mountains. These, as has been shown, 
are composed <>f the younger sedimentary rocks— the Nutzotin series. 
Still farther east the plateau is bounded by the St. Klias Range, the 
geology of which is but little known. The rocks of the Chugatch 
Mountains, a branch of the St. Klias Range lying to the south of the 
Chitina River, Schrader regards as probably Cretaceous. The beds 
exposed near Skolai Pas- I laves determined as Mesozoic or younger. 
At Yakutat Bay Russell" found Pleistocene beds, and at Lituya Bay 
Dall* reports phyllites and granite overlain by sandstones and con- 
glomerates, probably of Miocene age. Beds of Miocene age have 
been found between Controller Bay and Icy Bay on the southeast 
coast of Alaska. ' At Glacier Bay Reid and Gushing found Carbon- 
iferous limestones overlying phyllites of undetermined age. 



'The northern portion of the Canadian Rockies 1ms been studied by R, S. McConnell. See An 
exploration in the Yukon and Mackenzie basins: Geol.Surv. Canada, Vol. [V, 1888-89, Pt.IL 

- import on Paleozoic fossils from Alaska, by Charles Sehuchert: Seventeenth Ann. Kept. U. S. GeoJ, 
Survey, Pt. I, pp. 899-900. 

Nat.Geog. Mag., Vol. Ill, 1891-92, p. 167. 

• Seventeenth Ann. Rept.,l't. r, p. 784. 

•A reconnaissance in south western Alaska, by J. E. spun-; Twentieth Ann. Kept. r. S. Geol. Survey. 
Pt. VII. pp. 263-264 



BROOKS.] GOLD. HTM 

In the extension of the St. Elms Range to the southward Paleozoic 
and younger rocks have been found. The studies of the writer have 
shown that there are Carboniferous rocks along the northern margin 
of the range overlain by Tertiary or recent volcanics. The evidence, 
fragmentary as it is, points to the conclusion that while the coastal 
region of the St. Elias Range has been uplifted during Pleistocene 
times, as Professor Russell has shown, yet there was a much older 
protaxis, and that the range is in part made up of older rocks. That 
a part of the range is considerably metamorphosed compared with the 
coast belt is shown b} r the garnetiferous schists which have been 
reported among the glacial debris brought from the mountains, both 
at Yakutat and at Glacier Bay. The Coast Range, as has been shown, 
is a large mass of granite which was intruded in late Cretaceous or 
early Triassic times. 

MINERAL RESOURCES.' 



Most of the region under discussion lies without the gold belt of 
the interior of Alaska, and we did not see the rocks of the gold- bear- 
ing series until we reached the Fortymile basin. Much of the area 
included in the accompanying geological map is occupied by rocks 
younger than those which have made the Fortymile region and the 
Klondike so famous. This series of rocks, however, has been locally 
found to be highly mineralized and to carry some gold. It seems 
probable, from the best accounts, that the gold-bearing rocks of Atlin 
probably belong to the horizon of the younger sediments, as marked 
on the accompanying map — the Nutzotin series. There can be but 
little question that the rocks of the Porcupine gold district, in Chilkat 
River basin, belong to the Nutzotin series. It seems probable that the 
Shorty Creek district of the Kashaw River basin also derives its gold 
from this series. 

Considerable panning was done by our party as opportunity offered, 
and colors were occasionally obtained, but I am forced to the conclu- 
sion that the regions west of Dalton House, as far as the Fortymile 
basin, will never produce gold in commercial quantities. From 
accounts given by prospectors the Shorty Creek district docs not 
seem to have turned out as well as had been expected last year. Some 
brief statements in regard to this district were published by Mr. 
Russell L. Dunn, 2 from whom I quote as follows: 

What has generally been referred to as the Shorty Creek district is in the singular 
isolated mountain mass of metamorphic Jurassic slates lying westof Lake Desar- 
deash, 150 miles inland from Pyramid Harbor and accessible by the Dalton trail 
* * * Shorty Creek, though gold bearing and the locus of the first discovery, d< ies 

not seem to contain commercial values. * * * The district is, on the whole, not 

'See PI. XL. 'Mining and Scientific Press, Octobei 29, 1898, p. 125. 



374 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

one to which prospectors can go expecting to make a strike in the first season, nor 
even to anticipate very rich mines in. Miners, however, can make fair wages from 
many claims; incidentally they may discover something worth the attention of 

capital. 

Our expedition passed some 10 or 12 miles to the south of Shorty 
Creek, but I was unable to visit this locality. I am not inclined to 
agree with Mr. Dunn in regard to the Jurassic age of the slates, and 
these are represented on the accompanying map as belonging to the 
Nutzotin series, which is of Upper Paleozoic age. 

It will be seen that this belt of rocks, as a whole, is not gold bearing, 
yet it frequently is mineralized and in some places, as on Porcupine 
Creek, which will be described below, and possibly at Shorty Creek, 
may carry gold in commercial quantities. 

PORCUPINE (.OLD DISTRICT. 1 

This district lies on Porcupine ('reck, which joins the Klehini River 
about 35 miles from Pyramid Harbor and 7 miles below Pleasant 
Camp. During the brief visit made in .Tune, 18!Mt, only a few general 
facts could be gathered in regard to this district, for the upper 
courses of the creeks were then deeply buried in the snow. 

Near the mouth of Porcupine Creek there is a belt of white crystal- 
line limestone which strikes about northwest and southeast, and has 
steep dips, usually southwest. It is often much sheared and faulted, 
and the bedding is obscured. The belt is less than halt a mile wide, 
and above it i> a broader bell of (day slates which are usually highly 
contorted. The strike of the slates is about N. 20° W., and hence at 
variance with that of the limestone. There would seem to be an 
unconformity here, though the region is so much faulted that the 
structural relations can be determined only by a closer study than I 
was aide to give. 

In the stream gravels are found abundant pebbles of hornblende- 
granite, diorite, and quartz-diorite, and of some more basic rocks. 
None of these rocks were found in place and in only one locality were 
any dikes observed — about i' miles from the mouth of the creek, where 
a deeply weathered grayish dike rock was found cutting the slates and 
locally altering them to a hornstone. The dike, so far as could be deter- 
mined, was of dioritic character. 

There is a marked absence of quartz veins, both in the bed rock and 
in the stream gravels of Porcupine Creek. I found a few pebbles of 
vein quartz in the creek bed. but saw absolutely none cutting the 
slates. Calcite veins are. however, not uncommon in the slates and 
are frequently charged with pyrites. The slates, as a whole, are highly 
mineralized and assays from average samples showed that they carry 
t races of both gold and silver. Even though my visit was a very hur^ 

'See Pl.XLIX. 



brooks.] gold. :;7. r ) 

ried one. I saw enough to convince me that the gold of the placers was 
<lcii\ ed from these mineralized slates. Such being the ease, the extent 
of the district will depend on the width of this slate belt, which I was 
unable to determine on account of the snow. It is possible that the 
entire belt is not mineralized, and this fact should be borne in mind 
by prospectors. According to such facts as 1 was able to gather, lam 
led to believe that toward the headwaters of the creek there are large 
masses of granite and other intrusive rocks, probably similar in char- 
acter to those already referred to on Glacier Bay. Coarse gold has 
been found on MeKinley Creek, a tributary of Porcupine Creek. 

The placers that were being worked on Porcupine Creek during my 
visit were irregular benches which are formed of large bowlders more 
or less irregularly tumbled together. These stream benches can not be 
traced a great distance and are apparently due to the damming caused 
by rock barriers. The best pay dirt has been found above these rock 
barriers, among the large bowlders and gravels which have been 
deposited by the stream and contributed by the talus from the slopes 
of the valley. The presence of these very large bowlders, sometimes 
several feet in diameter, very much increases the cost of working the 
claims. The bars of the creek itself can be worked only at consider- 
able outlay, because of the difficulties of getting rid of the water. The 
Porcupine gold rates high in value as far as known, is rather pure, and 
the grains are usually very Hat, as would be expected of gold derived 
from mineralized slates. The pay dirt, so far as my observations go, 
is from 2 to 4 feet thick and lies on bed rock. A pan of gravel which 
1 washed out from one of the claims yielded about 20 cents in gold in 
5 different grains. 1 was informed that pans running 60 to 80 cents 
are not uncommon, and that the largest nuggets have been from $3 to 
$5 in value. Since leaving there I have been informed that the 
attempt was made to reach bed rock in the bed of the creek and that 
the miners passed through 18 feet of gravel without reaching the 
bottom. These gravels were said to have all carried values. 1 

Since my visit discoveries have been reported in the Salmon River 
Basin, east of Porcupine Creek, and on Glacier Creek, west of Porcu- 
pine. I have no definite information that there have been any placers 
of commercial value found outside of the Porcupine Valley, but would 
rather expect that the northeast and southwest extensions of the gold- 
bearing series would yield placers. The Porcupine district was dis- 
covered in dune, 1898, by Messrs. Mix and Finley, who located the 
Discovery claim about 2 miles from the mouth of the creek. 3 They 
are said to have taken out some $1,500 during the season. 

1 Mr. W. II. I'. .larvis, of Bennett, British Columbia, informs me that Since my visit 16 feel of pa\ 
dirt has been found on Porcupine Creek, giving S^O a day to the man. He estimates that the district 

produced some 860, (during the pasl season, but states thai there is noofflcia] basis for these figures. 

The output '" the coming season will undoubtedly be very much greater, as in 1899 much of the time 

and energy of the miners was given to prospecting rather than to the development of the claims. 

'According to another statement the credit of the discovery belongs to E. Haekley. 



37(5 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

The Porcupine district is easily accessible from the coast. Its open 
season is rather long, extending from June to September. The Dalton 
trail will enable miners to carry in provisions at no very great expense. 
Even if it is not so rich as some of the other placer regions of Alaska 
it possesses some advantages over those of the interior, and if it turns 
out as well as it promises we may expect it to continue to be a gold 
producer. 

FORTYMILE GOLD REGION. 

The first discoveries in gulch placers were made in the drainage 
basin of Fortymile River in 1886, and since that time the work of 
placer mining has been continuously carried on in the basin. This 
region has been reported on by Mr. Spun-, 1 and it is my purpose to 
give here only a few supplementary notes which were gathered on the 
recent trip. 

Fortymile River joins the Yukon about -"><> miles above the interna- 
tional boundary, and its mouth is, therefore, in Canadian territory. Its 
drainage basin is, for the most part, on the Alaskan side of the line, 
as are also most of its gold placers, so far as determined. The gold, 
as shown by Spurr, is derived from metamorphosed sedimentary rocks, 
which he divided into three formations. On the accompanying geo- 
logical map these are all included in the Kotlo series. The derivation 
of the gold is from quartz veins and from zones of impregnation, but 
up to the present time there have been no discoveries of veins reported 
which would warrant the introduction of mining machinery. 

Important creeks, from the standpoint of the gold prospector, are 
Napoleon. Chicken. Franklin, and Canyon creeks, as well as Nugget 
Gulch. All of these have produced gold in commercial quantities. 
There are innumerable smaller creeks and gulches which have been 
worked, many of them quite successfully, but most of them are not so 
rich as those that have been named. 

The important discovery of the past year has been Wade Creek. 
Wade Creek joins Walker Fork about 5 miles from South Folk. Its 
drainage basin lies immediately south of the trail leading from Frank- 
lin Creek to Steele Creek, and the valuable discoveries are said to 
have been made in the upper half of the basin. The pay streak is 
said to be rich but not very thick, and lies on lied rock some 12 or 14 
feel below the surface. Bench claims as well as creek claims are 
being worked. I was not able to visit this creek in person, and these 
facts were gleaned from various sources. As to the value of the 
claims I can give no definite information, but well-authenticated 
rumors state that fractions of claims had sold at from $30,000 to 
$40,000. The creek basin lies within the gold-bearing series and there 
seems to be a strong probability that this is the same series in which 

'Geology of the Yukon gold district: Eighteenth Ann. K.'i .t. t'. S. Geol. survey, Ft, III. Also, 
Explorations in Alaska in 1898. 



BROOKS.] COPPER. 'AIT 

the famous Klondike gold occurs. There is every reason 'to believe, 
therefore, that it has an important future as a gold producer. 

Like many of the creeks of the Fortymile Basin. Wade had long 
been prospected and had been reported as not carrying values. This 
is probably accounted for by the fact of the great depth to bed rock. 
The discoveries are said to have been made in March, 1899, and a 
steady influx of prospectors took place during the spring and summei 
months. The creek is easily accessible by a good trail from the mouth 
of Steele Creek, a distance of about 12 miles. Steele Creek can be 
reached by a trail which comes from Eagle City or by a small boat up 
Fortymile River from the Yukon. In the latter case prospectors will 
pass the United States custom-house at Sam Patch's, and will have to 
pay duty on their outfits unless they can prove that they were pur- 
chased in American territory. 

Though the Fortymile Basin has been more or less prospected dur- 
ing the last fifteen years, and especiall} 7 since the Klondike rush, yet it 
still offers a field for those who are willing to spend money and time 
in more detailed investigations. In the past the high price of pro- 
visions and the uncertainty and expense of transportation compelled 
the prospector to confine his attentions to deposits which would give 
immediate return. The conditions now are becoming more settled, 
more or less of the element of boom having been eliminated, and 
there is strong hope that careful prospecting will develop other gold 
placers in the Fortymile region. 

Of the other gold districts of this part of Alaska, Sixtymile River 
continues to attract a good many prospectors and to yield return for 
work expended, some of the claims on American Creek, near Eagle 
City, continuing to be gold producers. I saw a nugget valued at$l!»2 
which had been taken from a claim on American Creek in September. 
1899. 



Copper was probably the first metal which was reported from the 
Territory, for as far back as 1741 the Bering expedition found evi- 
dence of its use among the natives of the southeast coast of Alaska. 1 
It seems to have been extensively employed among the aborigines of 
Alaska, for many of the native languages contain a word signifying 
copper when they Lack a name for either iron or gold. The Copper 
River took its name from the fact that large copper deposits were 
reported to occur on its banks. 2 The natives of the Copper River, the 
Upper White, and the Upper Tanana have long been known to have 
access to native copper deposits, and it is probable that all the native 
copper in circulation previous to the ingress of the white traders was 
obtained from these natives. The natives used it for arrowheads and 

1 Dull, op. olt., p. 272. 

a Report on population and resources ol Alaska, p. 77. Tenth Census. 



378 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

later for bullets, and, it is said, for cooking- utensils, and when the 
coast was first visited by white men copper knives were said to be still 
in use. Not having any other metal than copper the} 7 adapted it to 
various purposes. The extent to which the intertribal trade in copper 
was carried out is witnessed by the fact that copper utensils are in use 
by the Haida Indians of Queen Charlotte Islands. 1 These copper 
utensils of the Haida Indians were obtained by barter with the Chil- 
kats, who in turn secured the copper from the Indians of the interior, 
probably of the White River. At the present day copper has a com- 
paratively limited use among the Alaskan Indians. They still use it 
for arrowheads, but these have been largely supplemented, by firearms. 
As most of them now use breech-loading rifles, they have no reason 
for manufacturing bullets of copper. Moreover, it is probable that 
the copper accessible to the natives lias been very largely exhausted. 
Their crude methods of digging enabled them to obtain it from the 
placers only close to stream cuttings, and at present larger pieces 
seem to be relatively rare. An interesting fact in connection with the 
native use of copper is that the placer deposits, which will be described 
below, are situated in gulches and valleys which were up to very 
recent time occupied by glaciers. As the glaciers gradually retreated 
they would leave the gravels uncovered and make the copper contained 
in them accessible. The time can not have been far distant when these 
valleys were filled with ice down to the main river valleys, and the 
copper contained in them can not have been in use by the natives more 
than a few centuries at most. 

KAINY HOLLOW COPPEB DEPO8IT8. 

On the accompanying route map (PI. XL) three copper belts are 

located. The most easterly of these is lo miles from Pleasant Cam]), 
at what is called Rainy Hollow. At this locality, which is about 3 
miles off the Dalton trail, near the head of Klehini River, 2 a copper 
vein was discovered late in the summer or early in the fall of L898. 
At the time of my visit much of this region was deeply buried in 
snow, and there was no opportunity for detailed investigations. The 
belt lies close to the contact of the Coast Range granite and the sedi- 
mentary rocks. The sedimentary rocks are quartz-schists, often cal- 
careous, striking about N. 60 E. and dipping very steeply southeast. 3 
The "Discovery" claim consists of two different veins, 2 feet and 



on: Geol. Surv. Canada, Report of Progress, 187S-79. 
2 This region is included in the Cassiar Mountain district of British Columbia. The name "Copper 
Mow division" has been suggested, but 1 trust that it has not y.t been accepted by the Canadian 
authorities. 

; Mr. J. P. Jarvis, of Bennett, British Columbia, who had opportunity to study this region after the 
snow left the ground, says that on the Montana (the Discovery claim | there are a number of stringers 
of bomite embracing a zone of 300 feel in the slates and calcitic rocks. Mr. Jarvis also reports large 
- <if zinc and lead from the same region. These, he states, occur in a belt about 3 miles long, 
running parallel to a belt of granite. The ore is said to run :!3 per cent lead, 22 per cent zinc, and a 
little copper. Some specimens sent to me showed zinc blende and galena with a calcitegangue. 



COPPER. S7\) 

18 inches in width. The copper minerals are bornite, chalcopy- 

rite, and malachite. The wall rock is a hornstone, which seems to 
have been silicified at the time of the intrusion of the copper- bearing 
solutions, and probably contains more or less copper-bearing minerals. 
The assays of copper ores from this region which were shown me by 
prospectors run from 20 to 55 per cent copper. From none of them. 
however, could I gel definite information as to whether they were 
average samples. My visit to this locality was simply the utilization 
of a day in which we had to rest our horses, and the observations were 
very limited. From talking to several prospectors who had been in 
the region for some, time and from examining- the specimens. I gathered 
that, there were other veins of relatively greater importance than the 
Discovery veins. The general appearance of the rocks, so far as my 
observation goes, is that a great deal of mineralization has taken 
place. Quartz veins carrying copper minerals are not uncommon in 
the metaniorphic slates and schists exposed along the Upper Klehini 
River. 

While my own investigations can not lead to any definite conclu- 
sions, yet 1 would regard the region as one worthy of attention by 
those seeking copper. It is easily accessible from tide water, being 
only some 50 miles from a good harbor, and could be easily reached 
by a railroad up the Klehini River, the highest point which would 
have to he crossed being about 2,000 feet in elevation. 

This mineral belt has not been traced west of Rainy Hollow. Tyr- 
rell, however, reports some copper pyrites bearing quartz from near 
Glacier camp, about 15 miles west, on the Dalton trail. 1 In the debris 
brought down by the O'Connor Glacier I observed much mineralized 
quartz carrying both iron and copper pyrite, and with it numerous 
fragments of white crystalline limestone as well as a variety of igneous 
intrusives. As the Rainy Hollow mineral deposits seem to be the 
result of contact phenomena between calcareous sediments and igneous 
locks, the westward extension of the contact would seem worthy of 
investigation. 

KLETSAN COPPER DEPOSITS. 5 

Kletsan Creek.'' from which this deposit takes its name, is an unim- 
portant tributary of the Upper White River, which joins the latter 
stream about 5 miles above the international boundary (see PI. L). 
This stream rises in a glacier which occupies the north slope of Mount 
Natazhat, a peak of the northern portion of the St. Elias Range. These 
copper deposits have long been known to the natives, and seem to have 
been the source of much of the copper which is in circulation among 
the Alaskan Indians. The marvelous tales told by the Indians living 

■ Summary Report, 1898, p. 16, Geol. Surv. Canada. 

*See PI. L. 

'Kletsan is the White River Indian word for copper. 



380 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

adjacent to this region of the wonderful "copper mountain" are 
important contributions to the earliest works of fiction concerning 
Alaska. 

Though stories of these rich copper deposits had long been known 
to the traders and pioneers of Alaska, the region was so inaccessible 
that no attempt had ever been made to visit the copper deposits up to 
1891. In that year Dr. Haves, in company with Lieutenant Schwatka, 
made a trip from Fort Selkirk to Skolai Pass, before referred to. 1 
In the course of this trip they were taken by the Indians to the 
copper deposits of Kletsan Creek. 8 In 1898 Mr. Jack Dalton, accom- 
panied by Mr. Henry Bratnober, visited Kletsan Creek and procured 
samples of the native copper from the placer deposits. 

The mountains lying to the south of Kletsan Creek are rugged and 
snow covered, the highest peaks probably reaching an elevation of 
15,000 feet. The streams all have glacial sources, and in their upper 
courses How through narrow rock-cut valleys. After leaving the base 
of the mountains they enter a broad gravel-tilled area in which they 
have incised deep channels. In general, this upland consists of a 
series of more or less well-defined benches interrupted by numerous 
small lakes and undrained depressions. These are. in part, of glacial 
origin, but are also, in part, due to the (.'lot ruction of the minor drainage 
caused by the deposition of a large amount of white volcanic ash, a 
description of which has already been given. The talus slope of the 
mountains is connected with the upland DV a gently sloping plain 
which owes its origin to a series of fan deltas formed by the streams 
that flow down the mountain gullies, the smaller ones only during the 
periods of rain. 

The geology of the region. 80 far as studied, is not very complex. 
Close to where the creek leaves its rocky floor there is exposed a belt 
of white crystalline limestone containing numerous fossils, which show 
it to he of Carboniferous age. Above the limestone are found a series 
of carbonaceous schists and shales, which sometimes approach an 
impure coal in character. Both the limestone and the shales are cut 
by dioritic and diabasic rocks, which are exposed along the creek in 
large areas. The diorites seem to be the older intrusions, and are in 
turn cut by diabases. As far as determined from the talus and stream 
gravels the mountains themselves are made up of effusive rocks, which 
overlie these unconformably. The Carboniferous rocks show great 
variety in strike and dip. In some places they lie nearly horizontal. 
and again they are sharply folded. The strikes vary from north and 
south to nearly east and west. The greenstones are jointed, but are 
not much sheared. The slates and limestones are locally faulted, but 



1 Nat. Gcog. Mag., Vol. IV, 1892, pp. 1-45. 

^ Another party of prospectors, under the leadership of Mr. Emmons, is said to have visited this 
copper belt in 1898. Several other parties of prospectors who reached the White River by way of 
Skolai Pass may also have visited the deposit. 



U S GEOLOGICAL SURVEY 



TWENTY-FIRST ANNUAL REPORT PART II PL. L 



SKETCH MAP 

Showing location of 

KLETSAN CREEKCOPFER DEPOSITS 










JS BIEN B CO LITM 



BB0OK8.J COPPER. 381 

usually the dips do uol exceed 20 and 30 . Near the contact with 
the greenstone the limestone is much altered, and the bedding planes 
are obscure. 

The placer copper deposits (all native) are contained in stream 
benches that owe their existence to rock harriers through which 
the streams have now cut their courses. The placer copper, as far as 
observed, is confined to a distance of about half a mile above the point 
where the creek leaves its rocky canyon. The placer copper is irregu- 
larly distributed on the bed rock in the crevices and also among the 
large bowlders. The nuggets found by the Indians who accompanied 
me seldom exceeded a few ounces in weight, though one was found 
which weighed 5 or 6 pounds, and another which I saw from the same 
legion weighed 8 or 10 pounds. The Indians dig the copper with 
caribou horns, and by this primitive method of mining must confine 
their efforts to the recent stream cuttings. 

As far as the limited time would permit a careful search was made 
for evidence as to the source of this native copper. An examination 
of the greenstones showed them to be traversed by an irregular system 
of joints, and calcite veins were observed which followed these joints. 
A careful examination showed that some of these veins carried native 
copper. These copper-bearing veins were found close to the contact 
with the limestones. Calcite veins were also found in the white crystal 
line limestone near the contact with the greenstones. A superficial 
examination of the greenstones showed that they a''e of a dioritic char- 
acter and are cut by a series of aphanitic dikes which are provisionally 
classed as diabases. The presence of amygdaloidal greenstones (prob- 
ably andesites) and some tufas among tin' stream gravels suggest that 
these basic intrusives may be the feeders or apophyses of outpourings 
of volcanic rocks. No other copper minerals except secondary mala- 
chite were found during the day spent in investigating the deposits. 
In the western extension of the copper belt amygdaloidal greenstones 
carrying amygdules of copper pyrite and various gangue minerals are 
not uncommon. To the east the Kletsan copper belt was traced only 
to the vicinity of the international boundary. Its eastern extension 
beyond this point, if it exists, is to be sought north of our route of 
travel. To the west the same zone seems to extend to the Upper White 
River. The streams entering the Upper White River flow from the 
south. As far as examined all carry copper colors, and the gravels are 
similar in character to the rocks of Kletsan Creek. 

TANANA-NAIJKSNA COPPEB DEPOSITS. 

A third belt of copper deposits was found along the route of travel 
between the Tanana and Nabesna. The region between the two belts 

is occupied by the young volcanic series, so that if the copper zone is 
present it is buried under these younger rocks. In this belt the 



882 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

evidence of the presence of copper was the same association of rocks 
as on Kletsan Creek and the presence of copper colors in the streams. 
Copper pyrite was found in the amygdaloidal greenstones, but not 
veins of native copper, as at Kletsan Creek. I am convinced that this 
is an extension of the same copper belt and that by further search 
copper deposits will be found. Native copper nuggets were brought 
to us by Indians who claimed to have found them in the region between 
the Tanana and the Nabesna. My investigations did not extend west 
of the Nabesna River, but I was informed by prospectors that "copper 
float" had been found in the Mentasta Mountains and also near the 
northeastern limit of the Alaskan Range. 

DEVELOPMENT OF COPPER. 

The question of the commercial value of these copper deposits is one 
that could not be settled in a hasty reconnaissance. The two copper 
belts are each about 40 miles long, with possibilities of their extending 
in both an easterly and westerly direction. As to the size and depth 
of veins which may be found no opinion can be o-iven, and it remains 
a question for future investigation. Such few faces as were collected 
in regard to the origin of the copper do not lead to the conclusion that 
the deposits would be of a superficial character. They are essentially 
contact phenomena. If a railway is ever built into the region it will 
naturally be constructed from Yaides. which is 200 miles awa\ and is 
the nearest harbor. Such a railway might also give access to the re- 
ported copper deposits ot the Chitina River. In any event I am of 
the opinion that (his upper region IS one that is worthy of careful 
investigation by the prospector and the capitalist. 



Coal has been reported from the region of the Upper White and 
Tanana rivers, but during our reconnaissance of the past season we 
saw no beds of coal which would be of commercial value. At a num- 
ber of places carbonaceous shales of Carboniferous age were found, 
but none of these were sufficiently pure to use for fuel. One of these 
was about 10 miles west of the Kershaw River, near our route of 
travel. At this locality beds of carbonaceous material some 20 or 30 
feet in thickness was exposed. Much of it had been altered to graphite 
by dynamic metamorphism. Near the upper end of Lake Kluane 
similar beds were found. On Kletsan Creek carbonaceous shales con- 
taining a little bituminous coal were found, but the coal was too impure 
to have any fuel value. The productive coals of Alaska have thus far 
been found in younger beds, and so far as known no coals of value 
have been found in the Carboniferous of this part of the continent. 
The outlook for coal is not encouraging, but should the region ever be 



bbooks.] ROUTES AND MODES OF TRAVEL. 383 

developed it is possible that locally some of the carbonaceous beds 
might have fuel value. 
The coals of the Upper Yukon have been described by Mr. Spun 

and others. They arc chiefly lignites of Tertiary age. Those that are 
accessible have been considerably mined for use on the Yukon River 
steamers. On the South Fork of Fortymile River considerable coal 
debris was found among the stream gravels. This was of a lignitic 
character, similar to that of the other Tertiary coals, and presumably 
the coal beds outcrop somewhere in the upper part of the drainage 
basin of the South Fork. 

ROUTES AND METHODS OF TRAVELING. 

The conditions of traveling in this region are similar to those which 
have so often been described elsewhere in Alaska. Probably the eas- 
iest journeys are made in winter when sledding is possible, with the 
use of dogs for draft animals, it is necessary to supply dog food 
either by carrying it along, which limits the length of the journey 
from the base of supplies, or by procuring dried tish, which, as a rule, 
can be had only at the Indian villages. Dogs are also used by the 
Indians in summer for carrying packs. Reindeer can probably be 
utilized in the uplands, where the reindeer moss is to be found. In 
the larger river valleys, as far as my observations go, the moss is not 
abundant, and the reindeer used for river trips would have to seek the 
uplands for food. The utility of reindeers as draft animals has been 
well demonstrated elsewhere in Alaska, and they have the advantage 
over dogs in that they find their own food. Up to the present time 
they have not been given a fair test as pack animals for summer use, 
but it seems possible that they may be better adapted for this purpose 
in this region than the horse or mule. 

In summer supplies are transported by back-packing, by pack ani- 
mals, or in boats. By the more primitive method of back-packing 
journeys are usually limited to three weeks, as this is the longest 
period for which the average man can carry provisions besides his 
blankets, etc. 

Horses can be used to advantage from about the middle of June to 
the first of September. Horses are preferable to mules because of the 
large amount of soft ground which has to be crossed. Our experience 
teaches us that "sawbucks" are better than '"aparejos," as the pack 
is less liable to slip off. In choosing a route for a pack train it is ad vis- 
able to keep at as high an elevation as possible, thus to avoid the swamps 
and thick timber of the lowland. We found the best grass above tim- 
ber line. 

A party making a trip in this region which involves crossing any of 
the larger rivers should carry a folding boat or the equipment for 



384 FROM PYRAMID HAEBOR TO EAOLE CITY, ALASKA. 

constructing one. We used a heavy, waterproofed canvas which we 
stretched over a framework built by the use of a few simple tools. 

Not much of the region is favorable for boating. Most of the larger 
rivers can be descended in boats at certain times in the year. Both the 
White and the Tatshenshini have been run in boats built by pros- 
pectors from whipsawed lumber. The Upper Tanana below the gorge, 
as well as the Nabesna, are favorable for the use of small boats, as are 
also the large lakes. 

DALTON TRAIL. 1 

This trail leaves the coast at Pyramid Harbor, situated near the 
head of Chilkat Inlet, where the depth of water is sufficient for any 
seagoing vessel. In 1899 no wharf existed and freight was taken 
ashore by lighters. 

The trail from Pyramid Harbor to Dalton House, in the interior, 
has been described in the itinerary. I will add that the hardest climb 
of the whole length of the trail is about do miles from the coast, near 
the police post. Here the crossing of a high spin- necessitates a climb 
of 1,000 feet, which could lie avoided by constructing a trail up the 
Klehini Valley. At Dalton House, which is about LOO miles from the 
coast, the trail turns northward, keeping to the east of Lake Deza- 
deash. and continues down the Kaskawulsh River, which drains the 
lake, to where this river makes its right-angled bend to the coast. It 
then crosses to the headwaters of Mendenhall River and thence con- 
tinues to the Nordenskiold. which it follows down to the Lewes River. 2 
The Dalton trail proper ends at the mouth of the Nordenskiold, but 
there is said to be a route all the way in to Dawson which has been 
followed by cattlemen with beef herds. 

The exploration of this route for a trail, and its subsequent estab- 
lishment, is due to the indomitable energy and perseverance of Mr. 
Jack Dalton. Mr. Dalton has done more than any other man for the 
exploration and development of this region. 

The trail usually opens between the middle of dune and the first of 
July. In the fall it can be used until about the middle of September. 
A permit having been granted by the Secretary <>f the Interior, the 
Alaskan portion of the trail is now a toll route. Below Pleasant Camp 
much money has been spent on the trail in road cutting, bridge build- 
ing, etc. 

ROUTES TO THE UPPER WHITE AND THE UPPER TANANA. 1 

The route followed by our party to the Tanana River is entirely 
feasible for a pack trail. The chief obstacles are the crossing of the 

'See PI. XL. 

-Many maps show the Dalton trail leading to Fori Selkirk, and in a previous publication I fell into 
the same blunder. The Dawson Range intervening makes such a route impracticable for pack 

trains. The Indians, however, are said to have a trail across tin-- range. 



ROI'TKS AND MODES OF TKAVKL. 



385 



large rivers. Only in the Nabesna and Tanana valleys did we have to 
do much trail cutting. The following table of distances has been com- 
piled from our map: 

Table of distances along route of expedition from Pyramid Harbor to Eagle City. 







Pleasant Camp 


40 




95 


Knskawulsh River 


130 


South end of Lake 












K 1 1 ■ t -;i 1 1 ( 'reck 


295 


Head of White River.. 


210 


Tanana Glacier 


340 


Nabesna River 


378 


I River nt 




mouth of Tetling 






430 


Franklin' Gulch 


520 




530 











A party intending to reach the Tanana or White from Eagle City 
would do well to take the Mentasta Pass trail from Franklin Gulch in 
the Fortymile Basin and reach the Tanana by way of the Khiltat. 
After crossing the Tanana it should make its way in a southeasterly 
direction and strike our trail near Tetling, or, what would probably 
be easier, follow the Mentasta trail to the Copper and then reach our 
trail on the Nabesna by the Batzulnetas trail. By this latter route it 
would be about 225 miles from Eagle City to the Nabesna. From 
Fort .Selkirk the overland route, which is said to he an old Indian 
trail, used by Schwatka and Hayes, is passable for pack animals. By 
this route it is about I7.~> miles to the Klutlan Glacier, and the 
Donjek is the only river of considerable size which would have to be 
crossed. From the mouth of the Nordenskiold, on the Lewes, a route 
exists to the White by way of the Nisling Valley. Mr. J. P.. Tyrrell's 
explorations of this route have already been referred to. On the 
accompanying map this route is continued across the White to the 
Tanana. This is entirely feasible except for the crossing of the White, 
which would he difficult. By descending the river to near the mouth 
of the Klotassin the crossing could probably he accomplished. The 
2\ GEOL, i'T 2 25 



386 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

distance from the Nordenskiold to the mouth of the Nisling is about 
175 miles. 

The shortest and probably the best route to the head of the Tanana 
or White is the Copper River route, which leaves the coast at V aides, 
on Prince William Sound. From this point a trail is now under con- 
struction by engineers of the United States Army, which is to avoid 
crossing the glacier. This proposed trail is to keep cast of the V aides 
Glacier and reach the Copper River at Copper Center, at the mouth 
of the Klutena. The rivers near the coast are said to have already 
been bridged, and the other streams, as the Konsina, will be crossed 
near their headwaters and will otter no serious obstacles. As the trail 
reaches the Copper on the outh side of the Klutena, and as the former 
river is usually crossed above the Klutena. the latter river will have 
to he crossed, which is no easy matter. It will he necessary to use 
boats in crossing both the Copper and the Klutena. After crossing 
the Copper the so-called Millard trail is followed to the mouth of the 
Slana: a turn to the eastward is then made to Batzulnetas, from which 
point a crossing can be made t<> the Nabesna, or across the Suslota 
Pa^s to Tetling. The distance from Yaldcs to the Nabesna by this 
route is about 200 miles. 

One of the routes into the interior which was tried during the 
Klondike excitement of 1898 and L899 crossed from Disenchantment 
\\:\\ . which is the upper end of Yakutat Bay, to the Alsek, and thence 
extended up that river and its tributaries. As a route into the interior 
it seems to have been a lamentable failure. Over 60 miles of glacier 
had to lie crossed to the Alsek. and when that river was reached it was 
found to be \ei\ turbulent and exceedingly dangerous to ascend. 
There was. moreover, an absence of fuel on the glacifir route, and onbj 
stunted alder on the Alsek. Some 300 prospectors are said to have 
started inland by this route, but probably not over 20 reached Dalton 
House, and those only after eighteen months of the hardest kind of 
toil and exposure. Several deaths due to exposure or to starvation 
have been reported from tin- region. 

RAILWAY ROUTES. 

Should the copper deposits of the Upper White and Tanana prove 
to he of sufficient extent to pay for a railway to them, the Copper 
River route would undoubtedly he chosen. Valdes, the natural ter- 
minus of such a railway, has an excellent harbor, which is open the 
entire year. A high divide would have to he crossed between Valdes 
and the Copper River. The next difficulty would he the crossing of 
the Copper River. The divides between the Nabesna and Copper and 
the Tanana and Copper is not over 3,000 feet. 

The route from Pyramid Harbor is one alone- which a railway could 
easily be built, except for the bridging of the several large rivers 



brooks.] TIMBER AND GAME. 387 

which must be crossed in reaching the White. The Alsek Valley may 
also offer a feasible railway route, but as there is no harbor at the 
mouth of the river it will probably never lie considered. 

TIMBER. 

Having hid neither the time for collecting nor the means of trans- 
porting botanical specimens. I must confine myself to a few general 
notes on the timber. The timber of the coast region has been fre- 
quently described. 1 The trees are of good size and abundant. In the 
Porcupine gold district the development of the placers is more or less 
hampered by the abundant vegetation, the roots of the trees often 
striking very deep. Along Lynn Canal there is very little timber 
above an elevation of 3,000 feet. Between Rainy Hollow, on the 
upper Klehini, and the Tatshenshini River the Dalton trail is above 
timber line for much of the distance. North and west of Dalton 
House the timber line gradually decreases from about 4,500 to about 
4,200 feet, varying somewhat according to local conditions. A stunted 
growth of willow and alder is still found above this up to an eleva- 
tion of about 5,500 to 6,000 feet. According to the statement of 
prospectors there are no trees except alder and willow on the Alsek, 
the first spruce forest being reached about 15 or 20 miles above the 
junction of the Kaskawulsh and Tatshenshini. The larger valleys, like 
those of the two forks of the Alsek and of the White and Tanana, are 
heavily wooded. The Tanana is especially noted for its large trees, 
whichare found up to 18 inches and 2 feet in diameter. The trees of the 
interior include several varieties of willow, alder, white birch, aspen, 
cottonwood. and spruce. : The spruce has the widest distribution of 
the trees valuable to the prospector. 

GAME. 



moose, cariliou (woodland), mountain goats, bighorns, wolves, and 
wolverines. The Indians still trap mink, beaver, and some foxes. 
though the fur-bearing animals are becoming relatively scarce. The 
skins of moose and caribou are used extensively by the Indians for the 
manufacture of clothing and other articles. The natives also depend 
on these animals in a very large measure for their food supply. Some 
silver-gray foxes are caught, seven skins having been shown to me at 
Dalton House. Wolf and wolverine skins are still in use among the 
Indians, as are bear skins. In winter the Indians kill the bighorn 
extensively, for at that time the cold and the dee}) snow drive these 
animals from the mountain tops, which they frequent in summer. 



•Those Interested in this subject are referred to the botanical notes i E Dr.Dawson, op. cit., pp 
186 190 

•These names are used in a popular sense as they are commonly accepted in Alaska, no ci 
having been made for determination. 



388 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

Moose and the larger bears are found, more especially along the val- 
leys of the rivers and lakes. The bears have not been definitely deter- 
mined by naturalists, but are classed by the prospectors as grizzly, 
silver tip, brown, and black bears. 

Caribou inhabit the regions at and above timber line. They are 
migratory, and in some years are very abundant, while in others they 
are almost entirely wanting. While game is usually fairly abundant 
in the more inaccessible portions of this region, yet it would be unwise 
for a party to depend on it for their food supply. Our experience 
shows that in some seasons game is exceedingly difficult to find. Wild 
fowl are very abundant along some of the larger rivers. Ptarmigan 
and grouse are usually plentiful at and above timber line. Salmon 
ascend the larger rivers except where there are rock barriers. 

CLIMATE. 

The meteorological data collected by our party are of too fragmentary 
a character and are distributed over too wide an area to be worth pub- 
lishing. Climatic records of the coast region of Alaska have long 
been made, and authentic data are now available in regard to the 
interior. 

The Lynn Canal region Is damp and has a comparatively mild 
climate. It is, however, colder than other parts <>f southeastern Alaska 
which are more directly subjected t<> the Influence of the Japanese 
current. In the Chilkat Basin there is a heavy snowfall, which is 
usually all gone below the snow line by the 1st of duly. 

The interior region Is much drier and colder. The snowfall is 
comparatively light, but by spring there is considerable accumulation. 
1 was informed that at Dalton House most of the snow disappears early 
in June. 

Before crossing the divide, about the 21st of June, we had consider- 
able rainfall. Clear weather prevailed until tow aid the end of July. 
From the 1st of August until we reached Eagle City we had many 
rainy and cloudy days, though the aggregate rainfall was not great. 

INHABITANTS. 

NATIVES. 

We saw very few natives during our journey, and are able, there- 
fore, to add no new facts concerning them. Those of Lynn Canal and 
Yakutat Bay, which have been frequently described, belong to the 
Thlinkit stock, which includes most of the Indians of southeastern 
Alaska. Those of Lynn Canal belong to two tribes — the Chilkats 
and the Chilkoots. They are semicivilized and live in well-con- 
structed houses in villages often of considerable size. They have 
long been known for their skill in weaving blankets and in certain 



beooks.] INHABITANTS NAT1VKS. 389 

other handicrafts. I have seen very creditable pieces of silver jewelry 

made by these Indians. They are usually thrifty and prosperous. 
During the long period when they acted as middlemen between the 
white traders of the coast and the interior or •"Stick" 1 Indians their 
livelihood was obtained chiefly by trade. Up to the time when the 
Hudson Hay Company established Fort Selkirk as a trading post, in 
1*47. they enjoyed a monopoly of the trade of the interior Indians. 
This monopoly they jealously guarded, as is shown by their raiding 
and burning Fort Selkirk in 1852. s Their trade with the interior 
Indians has almost disappeared, and they now earn a Livelihood by 
catching salmon for the canneries, and also drive a lucrative trade in 
the curios which they manufacture and dispose of at good prices to the 
many tourists who visit southeastern Alaska every year. 

The Chilkats are said to have waged a successful war with the 
interior Indians at a time not long distant and brought them to semi- 
subjugation. It is certain that the interior Indians stand in awe of 
those of Lynn Canal and will not visit the coast unless invited to do 
SO by the coast Indians or unless they feel sure of the protection of 
white men. We saw several villages and houses of Chilkats along 
the river and inlet bearing the same name. Klukwan, at the mouth 
of the Klehini. on the Chilkat River, is their most interior settlement. 

The interior Indians of the region visited by us belong to Atha- 
bascan stock and may be divided into three geographical groups — 
those of the Alsek Basin, who are subjects of Canada; those of (he 
White River Basin, who live largely in Canadian territory, and the 
Tanana Indians, who are on the Alaskan side of the line. 

The only permanent place of habitation that we saw after leaving 
the coast Indians was the village of Neskatatwen, near Dalton House, 
and therefore in the Alsek Basin. Here the Indians seem prosperous 
and live in substantial houses. They make their living by hunting, 
trapping, and salmon fishing. Closely related to these Indians are 
those of the village of Ilutshi, lying about 100 miles north of our 
route of travel. Indians from this district visited our camp on the 
Kaskawulsh. 

Of the White River Indians we saw no permanent habitations. 
While we were camped near Kletsan Creek a party of Indians visited 
us who claimed to be from Lake Kluane, but we saw no houses on the 
lake. Dr. Hayes 8 reported small Indian settlements on the Nisling 
and Kluane rivers. On the upper White we met a band of about 
20 Indians, but they claimed to have come from the Copper River 
and were evidently out on a hunting expedition. Nandles, Tetling, 
and Khiltat are the most important settlements of the upper Tanana. 
The Indians of the upper Tanana have easy communication with 



'This word belongs to the Chi k Jargon, long used for trading purposes along the const. 

■An exploration in Yukon district and British Columbia, !>y Geo. M. Dawson: Ann. Etept. 
Surv. Canada, 1887-88, p. 139B. « Nat.Geog. Mag., Vol. IV. p. 128. 



390 FROM PYRAMID HARBOR TO EAGLE CITY, ALASKA. 

those of the upper Copper River. The route which we followed to 
the White is said to be one much used by the Chilkats in their trading 
expeditions into the interior. In any event it Is certain that the 
interior Indians were hist supplied with the products of civilization by 
way of Lynn Canal. The Tanana Indians have been described in a 
previous report, already cited. We saw nothing- of the Indians of the 
Fortymile region. Their chief village is said to he Kechuinstnk. 
which is on the Tanana trail, near the head of the South Fork of 
Fortymile. 

WHITES. 

In the region explored by our party there were practically no white 
settlements except near the coast. Pyramid Harbor consists of a few 
houses and a canning factory. The latter in summer employs 50 or 60 
while nun. hut in winter the place is practically abandoned. Chilkat, 
which lies on the other side of the inlet from Pyramid Harbor, has 
a deserted canning factory ami a few houses, with one white family. 
I la i tie-.' u hich is on the other side of the neck of land separating Chil- 
koot and Chilkat inlets, is a settlement of considerable size. At this 
place l here are a mission, several stores, hotels, etc. Steamers daily 
make the trip to Skagway and return from this point. Many of (he 
sound steamers running to Skagway also stop at Haines. Haines 
is connected with Chilkat by a good wagon road, and a ferry crosses 
from the latter poinl to Pyramid Harbor. All three of these places 
are United State- post-offices. They depend for their development 
largely on the productiveness of the Porcupine gold district, which is 
about 30 miles inland. 

After Leaving the coast at Pyramid Harbor we passed several small 
settlements, some of which will probably have more or less perma- 
nency. At Walkerville were one or two buildings and L5 or 20 tents. 
Sunrise included a single log building. Porcupine City, near the 
mouth of Porcupine Creek, has several substantial buildings, includ- 
ing two -tores and a sawmill. Prospectors' camps are also to he 
found along the entire length of the creek. 

At Pleasant Camp." which is beautifully situated on a bluti' over- 
looking the river, are one of Dalton's trading posts and a northwest 
mounted-police post. The latter at the time of our visit included one 
officer and seven privates. A number of substantial buildings have 
been erected, and the site is probably one of the finest in the entire 
region. 

Going inland along the Dalton trail we found a number of pros- 
pectors' camps in and near Rainy Hollow. These were then only 
temporary structures, but should the copper prove to have commercial 
value this will undoubtedly become an important place. Beyond 

i This was formerly known us HainesS Mission. 2 See PI. XLI, A. 



BBOOKS.] INHABITANTS WHITES. 391 

Rainy Hollow until Dalton House is reached there are do white settle- 
ments of any kind. At Dalton House is another trading post belong- 
ing to Mr. Dalton and in charge of a white man. There are also two 
members of the Canadian mounted police stationed there. The Indian 
village near at hand has already been referred to. There is said to be 
another trading post in charge of a white trader near Hutshi. 

Between Dalton House, in the Fortymile Basin, and Franklin Gulch 
we saw no white settlements whatever, though the Indians told us that 
the United States Army had established a post at Mentasta Pass. In 
the Forty mile Basin there are a great many white men and several 
settlements of considerable size. At Franklin Gulch there are Lo or 
20 substantial loo- cabins. Since the rush to Wade Creek, already 
referred to, a great many prospectors have come into this part of 
Fortymile Basin, and their cabins can be found in many gulches. On 
the lower Fortymile we passed a number of log houses, the largest 
settlement being at the international boundary, where there is now a 
United States custom office, a hotel, and a trading post. 

Fortymile Post, at the mouth of the river of the same name, is a 
village of considerable size. The Canadian police headquarters, 
known as Fort Cudahy. IS a short distance below, on the Yukon. 
Eagle City, some 50 miles below, promises to be the most important 
settement on the Alaskan side of the line on the upper Yukon. The 
site is well chosen and is on the banks of the Yukon, just below the 
mouth of American Creek. The sanitary conditions are much more 
favorable than at most of the mining camps on the Yukon. The vari- 
ous trading-post companies have put up substantial stores and ware- 
houses, and the Government has erected large barracks for the 
company of soldiers now stationed there. The Nome rush of 1899 
retarded the development of Eagle City very much, and, like most of 
the other towns on the Yukon, it for a time became almost deserted 
except for the Government officials and the agents of the larger trad- 
ing companies. 



A RECONNAISSANCE OF THE CHITINA RIVER AND 
THE SKOLAI MOUNTAINS, ALASKA 



OSCAK ROIIX 



CONTENTS 



Page. 

Introduction - 399 

Previous exploration - -. -- 400 

Work of explorers ... 400 

Work of prospectors 401 

Alaska Exploring Expedition No. 2 402 

Discover}' of the new route 403 

l >bjed of the expedition IC3 

I 'la n~ and preparations 404 

Itinerary 405 

Valdez to the Chitina 405 

Chitina to the Nizina < rlacier 406 

over the Nizina and Tanana glaciers to Copper River 407 

General features 408 

Topography 408 

Valdes and the coast mountains 408 

I !( »pper River Valley 408 

( ihitina River Valley 409 

Nizina River 409 

The coast mountains south of the Chitina River 410 

Wrangell Mountains 410 

( ilimate and seasons 412 

Timberand vegetation - 414 

Animal Life 415 

Trail- 415 

Tonsinaand Lower Copper River 415 

To the Kotsina River 416 

Along the Chitina River 41ti 

Skolai Pass 417 

Upper Copper River Valley 417 

From the Copper to the Nabesna and Tanana 417 

Pack trains 4 IS 

Geology 418 

Preliminary statement 418 

Valdes to the Tonsina River 419 

The Kotsina section 420 

From the Chitina River to Kennicott Glacier 422 

The Ni/.ina-Tanana section 425 

( reneral relations 425 

Nikolai greenstone 420 

Chitistone limestone 420 

McCarthy Creek shales 420 

Faulting and folding in Chitistone limestone and McCarthy Creek 

shales 427 

Other rocks 427 

395 



396 CONTENTS. 

Geology — Continued. Page. 

Basic volcanic rocks 42!> 

Acid igneous rocks 430 

Relative age and probable correlation 431 

Table of provisional correlations 433 

Probable structure of the area 434 

General structure - 435 

Mineral prospects 436 

Gold - 436 

Copper 437 

Appendix 439 



LLUSTRATIONS. 



Page 

vn; LI. Outline map of Alaska - 400 

LII. Geologic map of the Wrangell Mountains area.' 404 

LIII. Summit of the Nizina-Tanana Glacier, looking west 406 

LIN'. Summit of the Nizina-Tanana Glacier, looking east 408 

LV. Foot of the Xanana Glacier 410 

LVI. Crevasses in the Tanana Glacier - . 412 

LVII, Mountains south of Kennicott Pass 424 

LVIII. View of Kennicott Glacier 420 

LIX. .1, Folding in Chitistone limestone; B, Amphitheater form of 

erosion 428 



A RECONNAISSANCE OF THE CHITINA RIVER AND 
THE SKOLAI MOUNTAINS, ALASKA. 



By ( )sgar Rohn. 



INTRODUCTION. 

The following report is based upon field work done by me during 
the season of 1899, while I was in charge of a detachment of the Cop- 
per River Military Exploring Expedition. This expedition, sent out 
by direction of Assistant Secretary of War G. D. Meiklejohn, was 
commanded by Capt. W. R. Abercrombie, Second United States 
Infantry. The object of the subexpedition in my charge was to 
explore, for the War Department, the unknown area south and east of 
the Wrangell Mountains, and this report is prepared for the United 
States Geological Survey by permission of the Assistant Secretary 
of War, to supplement an earlier and less complete report to the War 
Department. 

I wish to acknowledge my indebtedness to the Director of the Geo- 
logical Survey for the opportunity to make this report, and to the 
Assistant Secretary of War for permission to do so. I am also par- 
ticularly indebted to Professor Van Ilise, to Mr. Willis, and to Mr. 
Spurr for aid in preparing the manuscript, and to Mr. Goode and 
Mr. Peters for help in preparing maps. Special recognition is here 
due to Mr. Arthur IT. McXeer, the young man who consented to con- 
tinue with me over the Nizina Glacier when the members of the party 
were unwilling to do so, and to whom 1 am. therefore, indebted for 
not having to abandon the trip at the foot of the Nizina Glacier. 

The area covered by this report is attracting attention on account of 
the fact that it affords an opportunity for reaching the interior of 
Alaska from a good port by a route entirely on American soil, and 
because it gives promise of containing mineral wealth. The route 
from Valdes to the interior is indicated in red on the general map of 
Alaska (PI. LI) which accompanies this report. On this is also indi- 
cated the area included in the detailed map (PI. LII). 

399 



400 CHITINA EIVER AND SKOLAI MOUNTAINS. 

PREVIOUS EXPLORATION. 

WORK OF EXPLORERS. 

Prince William Sound, formerly known as Chugach Gulf, was dis- 
covered by Captain Cook in 1778. Soon afterwards it was visited by a 
number of English, Spanish, and Russian explorers, among whom were 
Fidalgo, Vancouver. Quadra, and Nagaief. Copper River was first 
seen by Nagaief in 1781, and first ascended for a short distance by 
Bazanof in 1803. l The exploration of the stream was next undertaken. 
by a party of the Russian-American Company, who in 1813 ascended 
it for a short distance tor the purpose of trading with the natives,' 2 and 
five years later Serebrennikof, with a party of Russian explorers, suc- 
ceeded in reaching a point above the mouth of the Tazlina River, 
where, however, he and his entire party were massacred by the natives. 3 
Nothing was done from this time until L882, when ('. (i. Holt, a trader 
in the employ of the Alaska Commercial Company, readied Taral. 
Two years later Captain A.bercrombie, of the United States Army, made 
an effort to ascend the river, but did not succeed in getting farther 
than Miles ( i lacier. ' 

In 1885, the year follow ing Captain AJbercoiiibie's attempt to ascend 
the river, Lieut. Henry T. Allen, of the United States Army, made one 
of tlie most remarkable exploration trips recorded in Alaskan his- 
tory.' He ascended the Copper to Taral. From here he reached the 
Nikolai house, on the Chitina, by portage, and returned down the 
Chit ina by boat. He then made his way up the Copper to Batzul- 
netas. And from here, crossing the Mentasta Mountains to the 
Tanana River by \\a\ of Suslota Pass, he descended the river to the 
Yukon. Though he and his parly practically lived oil the country 
and suffered great privations and hardships, he was not content with 
his great success, hut ascended the Koyukuk for a distance of several 
hundred miles before returning home by way of the Yukon and Si. 
Michael. 

To Lieutenant Allen we are indebted for the first reliable maps and 
information regaining the Copper, Chitina, and Tanana rivers, and 
the group of mountains surrounding the active volcano known as 
Mount Wrangell. In L898 a party of the United Stales Geological 
Survey, in charge of Mr. W . J. Peters, accompanied l>y Mr. A. H. 
Brooks as geologist.'' explored and mapped the Tanana River from a 
point where it leaves the mountains to its confluence with the Yukon. 

In 1891 Lieut. Frederick Schwatka and Dr. C. Willard Hayes' 

'Alaska and its Resources, by W. U. Dall, pp. 317-821. 

^Bancroft's History til Alaska, p. 526. 
■'Alaska and its Resources, by W. II. Dall, ]>. '272. 
< Reconnaissance in Alaska, Lieut. II. I . Alii n, 1885, ]>■ 2:;. 
5 0p. oit. 

•■■Explorations in Alaska in 1898; U. 8. Geol. Survey, p. (.1. 

; An expedition through the Yukon district, by C. W. Hayes: Nat.Geog. Mag., May 15, 1892, Vol.1 V 
p. 120-127. 



U. S. GEOLOGICAL SURVEY 




TWENTY-FIRST ANNUAL REPORT PART II PL. LI 




rohm.] WORK OF PBOSPECTOB8. 401 

entered the Chitina Valley through the headwaters of the White 
River, by way of the Skolai Pass, which they discovered and named. 
Reaching the headwaters of the Nizina River, they built a boat in 
which they ran down the Nizina to the Chitina, then down the Chitina 
to the Copper, and along- this to the coast. Considering the diffieul- 
ties which both Lieutenant Allen and Dr. Hayes encountered, their 
maps and observations are remarkably accurate, though they are, of 
course, restricted to the immediate vicinity of the respective routes 
traveled. 

WORK OF PROSPECTORS. 

The general rush to Alaska in the spring of 1898, due to the Klondike 
discoveries of the previous year, resulted in the landing of between 
4,000 and 5,000 prospectors with their outfits at the head of Valdes 
Bay during the months of March, April, and May of that year. A 
route was supposed to exist from here to a point on the Copper River 
above the rapids and can} T ons reported by Lieutenant Allen, but no 
exploration of this route had ever been recorded, and no information 
regarding it could be obtained. 

The general impression among these adventurers, that the interior 
was a great field of treasure and that beyond reaching it little else was 
needed to enable them to gather a fortune, spurred them into attempt- 
ing to cross the glacier that occupies the only break in the moun- 
tains surrounding Valdes which seemed to give promise of leading 
from the bay into the interior. This, subsequent developments proved 
it to do, butthe difficulties which it presented were very great. With 
the thermometer at 40° to 50° below zero, in the fierce storms which 
only polar glaciers can give birth to, and with fuel at $1 a pound, 
outfits were sledded over a course that in places required hoisting by 
means of rope and tackle. 

Beyond this glacier, which is now known as the Valdes Glacier, a 
swift and pow< it'u 1 stream, which proved to be that named by Lieu- 
tenant Allen the Klutena, was found to lead in a general northeasterly 
direction to the Copper River, and by carrying their goods down this 
in boats the more fortunate reached Copper River. Many of those 
who reached Valdes never landed; many more turned hack disheart- 
ened at the glacier; others succeeded in crossing the glacier only to 
lose their outfits in the swift and treacherous waters of the Klutena, 
and only a minor pari of the crowd that landed ever got far beyond 
the mouth of the Klutena, where a winter camp sprung up which was 
called Copper Center. Nearly all of those who went beyond Copper 
Center were headed for the Yukon by way of the Mentasta Pass and 
the Fortymile River. Mentasta Pass was reached by two general 
routes— one by "tracking" or "cordelling" boats up the Copper 
River, the other by an overland route leading from Copper Center 
21 GEOL, l'T 2— •_'*'> 



402 CHITINA RIVER AND SKOLAI MOUNTAINS. 

along the foot of Mount Drum to the mouth of the Slana, known as 
the Millard trail. At the mouth of the Slana the two routes eon- 
verged and, following along the eastern bank of this stream, led to 
Mentasta Pass. A number of parties made this trip and the routes 
were well established. One party even made the trip to the Yukon 
and return in the course of the season. 

The major portion of each man's time was spent in traveling and 
transporting goods, and, considering the number of men who reached 
the interior, comparatively little prospecting was done. Such as was 
done was confined to the immediate vicinity of the routes named and 
to the Copper River from Copper Center to the coast. The short 
streams tributary to the Copper heading in the Wrangell Mountains 
were explored to some extent, but the Chitina was ascended only a 
very short distance. All of the mineral prospects discovered by the 
season's work were practically confined to those of Quartz Creek, a 
southern tributary of the Tonsina. This was discovered in August, 
but was not reported until later in the season, when a general stam- 
pede for the area occurred. 

The discouraging prospects led many to leave the country at the 
approach of winter. Some returned over the glacier to Valdes, 
but more went down the Copper River to the coast in boats. Of 
those who had sufficient provisions and were determined to explore 
farther the greater number wintered at Copper Center, at Quartz 
Creek, and at Valdes. A few were scattered in isolated camps along 
the Klutena and along the Copper River below Copper Center. 

ALASKA EXPLORING EXPEDITION NO. 2. 

The War Department, in an endeavor to find an all-American route 
to the interior of Alaska, put three parties in the field in the spring 
of 1898; one at Cook Inlet, one at Prince William Sound, and a third 
at Lynn Canal. The Prince William Sound expedition was in charge 
of Capt. W. R. Abercrombie, Tinted States Army. It landed at 
Valdes in April, and spent the earlier part of the season examining 
the coast of Prince William Sound and the different bays or fjords 
adjacent to it. In August a start was made for the interior. A 
detachment of the expedition in charge of Mr. F. C. Schrader, 1 a 
member of the United States Geological Survey, detailed with the 
expedition, crossed the glacier with a pack train and reached Copper 
Center by the then well-established trail along the Klutena River. 
Here the party divided, one detachment, under Lieutenant Lowe, 
going northward to Mentasta Pass and finally reaching Forty mile; and 
the other, in charge of Mr. Schrader, going down the Copper River. 
Taral was reached with the horses. These were then abandoned and 



l A reconnaissance of a part of Prince William Sound and the Copper River district, Alaska, by 
F. C. Schrader: Twentieth Annual Rept. V. - Geol. Survey, Ft. VII, pp. 321-423. 



kohn] OBJECT OF THE EXPEDITION. 403 

the journey was continued by boat to the mouth of the Tasnuna. 
From here, by back-packing up the valley of the Tasnuna, Mr. 
Schrader succeeded in reaching the valley of the Lowe River, and 
along this he made his way back to Valdes. 

The year's work showed that beyond the coast mountains the country 
is open and affords splendid opportunities for the construction of pack 
trails and railroads; but that, unless a way of avoiding all glaciers 
could be found through the coast mountains, a general route from 
Valdes to the interior was not feasible. 

DISCOVERY OF THE NEW ROUTE. 

The finding of placer prospects attracted prospectors from the 
Klutena River to Quartz Creek. From here they worked over a low 
divide into the valley of the Kanata. Finding a few colors of gold in 
the gravels of this, they followed it to its confluence with the Chena, 
and worked up along the banks of the latter for a distance of 12 to 15 
miles. The route from this point to Valdes being very circuitous, a 
man named Johnson who, with a companion, made monthly trips with 
the mail from Valdes to the various camps, attempted to find a more 
direct one. He made several attempts to find his way from the Chena 
out to Valdes, in one of which his companion perished from freezing. 
Johnson, however, persevered and finally succeeded in reaching the 
Lowe River Valley by way of what is now called the Lowe River 
divide. This was the final step that completed the all-important route 
through the coast mountains and made possible what now promises to 
be the gateway to the interior. 

When Captain Abercrombie's expedition landed in the spring of L899, 
Johnson's discovery had become generally known, and several parties 
of prospectors who had landed early in the season were already at the 
summit of Lowe River divide, bound for Quartz Creek with their 
season's supplies. 

OBJECT OF THE EXPEDITION. 

No satisfactory placer prospects having been found in 1898, the 
mountainous region east of Copper River attracted the attention of 
those prospectors who remained through the winter, as affording the 
most favorable field for further work. Copper deposits were known 
to exist somewhere in this area by the fact that the natives repeatedly 
brought specimens of this metal to the trading stations on both the 
coast and the Yukon, and to these deposits tiie attention of prospectors 
was drawn by the opening of copper claims on Prince William Sound 
during the previous year. The explorations of Lieutenant Allen and 
Dr. Hayes showed that the area is exceedingly rugged and difficult of 
access, and that it forms the divides between four meat streams. But 



404 CHITINA RIVER AND SKOLAI MOUNTAINS. 

beyond this nothing was known of it. Under these conditions it was 
most important to the work of the prospectors and the development 
of the area, and of much interest from a geographic and scientific 
standpoint, that the area should be explored and mapped, and its true 
nature and accessibility be determined. To undertake this work, a 
detachment of the expedition was detailed by Captain Abercrombie 
and put in my charge. The plan decided upon was to work up the 
valley of the Chitina with a pack train, and, if possible, to cross to 
the headwaters of the Copper. If it was found impossible to pro- 
ceed with the horses, they were to be left, the trip to be continued by 
back-packing or sledding. Upon reaching navigable waters on the 
Copper River it was intended to build rafts or canoes, and by means 
of these to run down Copper River to Copper Center. 

PLANS VXD PREPARATIONS. 

The general experience of Alaskan explorers lias shown that, as a 
rule, each member of a party must cany his own provisions, and that 
increasing the number of men in a party is merely increasing the amount 
of provisions necessary and adding to the difficulties. The area to be 
explored was known to be very rugged and forbidding, and one in which 
back-packing would probably have to be resorted to. It was therefore 
decided to select instruments for cartographic work and the necessary 
provisions and camp outfit with a view to the least weight and bulk 
that could possibly be made to serve the purpose. The party was 
accordingly restricted to tour men. I was to take charge of both car- 
tographic and scientific work ; two packers, J. V. Place and H. H. Fitch, 
were to handle the pack train, and dohn Fohlin was to act as cook and 
camp man. The instrumental outfit for cartographic work consisted 
of a Johnson's improved traverse plane table with a small open-sight 
alidade, a small sextant with an artificial mirror horizon, an aneroid 
barometer, and two high-grade watches. In addition to a very light 
camp outfit, two 11-foot canvas folding canoes were carried to provide 
for crossing glacial streams. It was found thai these were too small 
and that one larger boat would have been more serviceable. No pro- 
vision was made for crossing glaciers, but fortunately we were able to 
secure two sleds at the Nikolai House. 

Not being provided with the fuel and cooking arrangements ordi- 
narily used in glacial work, we prepared as much bread and bacon as 
possible before starting over the glacier, and carried with us dry spruce 
timber with which to prepare a little coffee and oatmeal daily. Though 
this arrangement sufficed to carry us through, it did not fail to show 
us the inadvisability of undertaking an extended and uncertain glacial 
trip without suitable and adequate provision for preparing food on the 
way. It is, however, almost equally undesirable to cany coal oil and 
lamp stoves on a long overland trip when there is only a possibility 



U. S GEOLOGICAL SURVEY 



HKJHMKNTAHY 



- nn is i . im i.imi-.s ni\i; \n akiiii - n 

I.IMKM'OM-". I-X)li MATH INS AXn Kr.sKl 1 

I'Al.l-A.Z.Hi !N i;j NKtiAL shai.i:s 



N1HTI.YINC USED .1:1 1 ',1. 



TCKNNIOi'l I-SKII1KS KnrsINA 

.IMMKXTS .irr.ANS.ll ..UKT.V.KI.rs ( ■OXIW.DMKHAI'h I'N< I.ASS1F 

1 SERIES 



GEOLOGICAL SKETCH MAP 

OF 

WRANGELL MOUNTAINS AND ADJACENT AREA 

by 

OSCAR ROHN 
1899 



Contour interval approximately 500 feel 

Datum is mean Bea Level 
Probable drainage not surveyed 




TWENTY-FIRST ANNUAL REPORT PART II PL 




rohh.J VALDES TO THE CHITINA. 405 

that there will be occasion to use them. This can be avoided by pro- 
viding a small folding sheet-iron charcoal pot. Charcoal being very 
lie-lit. sufficient tor a considerable time in an ice or timberless area could 
be carried, and this could be readily prepared at the point of beginning 
such part of the trip. 

ITINERARY. 

The new route to the interior, as has been explained, had been dis- 
covered and its practicability determined when Captain Abercrombie 
landed with bis expedition in the spring of 1899. He therefore directed 
his attention at once to building a trail through Keystone Canyon, 
on Lowe River, about 12 miles above its mouth. The prospecting 
parties mentioned as having gone in earlier in the season had passed 
through the canyon on the ice. It was now. however, too late to do 
this, and the necessity of building a trail around the canyon delayed 
our start until the 18th of June. In the meantime the area about 
Valdes and tlie shore of the bay were carefully examined and mapped 
in detail, and a series of soundings were made in the bay. 

VALDES TO THE CHITINA. 1 

In company with a detachment of the Copper River Exploring Ex- 
pedition conveying the United States mail inspector from Valdes to 
Eagle City, on the Yukon, and the United States mail contractor and 
several parties of prospectors, we left Valdes on the 18th of June. The 
first day's route lay along the north bank of Lowe River to Keystone 
Canyon. This, a deep, rocky gorge by which Lowe River breaks 
through the mountains, was passed by way of the new trail, just built. 
Beyond Keystone Canyon the course lay up the north side of the Upper 
Lowe River Valley, a distance of about 7 miles, to Lowe River divide, 
which was crossed at an altitude of 2, 6(H) feet. From here a journey of 
about 7 miles in a general northeasterly direction took us to the Chena 
River. Thus far we had traveled over a trail prepared by prospectors 
who. as has been said, came in earlier in the season. These we found 
encamped at the head of the Chena River awaiting our arrival, and 
from hereon it became necessary to pick and prepare a trail suitable 
for further progress. In this I was assisted by Mr. R. F. McClellan, 
who was in charge of a large prospecting party. 

After following the valley of the Chena as best we could for a dis- 
tance of about L5 miles to its confluence with the Kanata, we proceeded 
up the right bank of the latter stream, and by way of a divide known 
as the "Drop" we reached Quartz Creek, which we followed to its 
mouth at the foot of Tonsina Lake. From here part of the out lit was 
taken to Copper Center by way of the Klutena River, arrangements 
being made to have it broughl down Copper River by boat. While 
this was being done, the I rail leading from Tonsina Lake to the ( 'opper 

i This name has been spelled in various ways. For Alaskan names see pp. 187-509 of tiii- report. 



406 CHITINA EIVER AND 8KOLAI MOUNTAINS. 

River was cut out and marked,, .so that by way of it the pack train 
could be taken to Copper River on its return to Tonsina Lake. Cop- 
per River was crossed a little above the mouth of the Tonsina. From 
here the outfit was carried to the mouth of the Chitina in boats, and 
the horses were driven down the river along the eastern bank. 

While the relay trips of the pack train necessary to bring the outfit 
to the Copper River were being made, a side trip of ten days was made 
up the Kotsina River by way of the trail from Copper River. 

CHITINA TO THE NIZINA GLACIER. 

From the mouth of the Chitina, which we reached on July 21, we 
followed an old Indian trail leading along the northern side of the 
river. This trail was very old and very little used, but having secured 
an Indian guide acquainted with it, we had no difficulty in following 
it. It led us directly to the mountains, and up into these along the 
western bank of the Kuskulana River for a distance of ."> or 6 miles. 
Then crossing the river near tin- foot of the glacier, we entered a narrow, 
transverse gulch leading away from it into the mountains eastward. 
After rising rather steeply for some time, this gulch opened out into 
a broad valley, which we followed in a general southeasterly direction- 
for about 15 miles. Here we encountered the second stream of con- 
siderable size, known as the Lachina. The Indian trail leads off south- 
ward at this point, and we decided to abandon it and attempt to continue 
through a narrow valley leading eastward through the mountains. 
This valley, which is transverse to the general drainage of the area, 
was found to lead out upon a large glacier for which I propose the 
name of Kemiieott Glacier. 1 This glacier being too rough to cross 
with the pack train, it was necessary to work around the foot of it for 
a distance of about 8 or 10 miles. Beyond this the valley of a small 
stream opening into the glacial valley enabled us to continue in a gen- 
eral northeasterly direction, and finally, after crossing a mountain 
range at an altitude of 6,500 feet and after descending 4.00(1 feet on a 
very steep and difficult slope, we succeeded in reaching the valley of 
the Nizina River. 

We were traveling along the southern side of a very high range of 
mountains extending east ward from Mount Blackburn. We had thus 
far been unable to find any opportunity to cross. On the Nizina, 
however, we found the lowest divide yet seen, and, while it was occu- 
pied by a large glacier, it seemed to offer the only opportunity of 
crossing, and we decided to attempt to cross here. We continued up 
the valley of the Nizina to a point about ?> miles above the foot of 
the glacier. Dr. Hayes, 3 who first saw this glacier, regards the Nizina 

i Named in honor of Robert Kennieott, a pioneer in Alaskan exploration, who, us director of the 
scientific corps of the Western Union Telegraph Expeditions 1865, established the identity of the 
Kwikpakof the Russians and the Yukon of the English, and who sacrificed his life in the undertaking. 

= Op. eit. 



roiin] OVER THE NIZINA AND TAN ANA GLACIERS. 407 

River as heading in Russell Glacier and crowded out of its course by 
tins, which he calls a great triple glacier. It will be referred to as the 
Nizina Glacier. 

OVER THE NIZTNA AND TANANA GLACIERS TO COPPER RIVER. 

Finding it impossible to proceed farther with the horses, the party 
was divided, I and Mr. A. H. McNeer 1 continuing over the glacier, 

while the remainder of the party returned to Valdes with the pack 
train. 

'Idic glacier would be difficult to cross at any time, hut at this season 
of the year it was especially so. By exercising all possible care and 
awaiting our opportunity, we succeeded in making our way over the 
summit, and at the end of fifteen days reached the foot, on the opposite 
side. The summit was found to be over 8,000 feet above the sea. and 
the length of the glacier from foot to foot along the route which we 
traveled was about 47 miles. 

I )uring the trip over the glacier the storms which are almost constant 
on the summit at that time of the year, the difficulties of traversing 
glacial ice, and snow-blindness absorbed our attention and left us no 
time to speculate on what drainage we were reaching. When, how- 
ever, the glacier had been crossed, the latter became the all-absorbing 
question. After following the stream which headed in the glacier for 
a distance of 12 or 15 miles in a northeasterly direction, and finding 
that it led out of the mountains in a direction almost due east, we 
became convinced that it was the Tanana River, and we decided to 
make a portage through a gap in the mountains to the west, by 
which we hoped to reach what we felt sure was a branch of Copper 
River. At the end of a seven-days' packing trip we readied a large 
river, winch, however, proved to be merely a branch of the Tanana. 
called by the natives Nabesna. 

The lower Nabesna and its confluence witli the Tanana are indicated 
on Mr. Peters \s map of 1898. But it is here shown to head on the east- 
ern side of the range, which we found it to break through. 

On the mountain at the foot of the Tanana Glacier we found two 
stone cairns, and on the river bottoms some miles below we found 
horse tracks. At the time, we supposed these to have been left by 
prospecting parties who had started for this area in the spring with 
pack trains. Since returning, however, we find that the cairns are 
monuments left by the Peters party of the United States Geological 
Survey, who passed through this valley some weeks before us. We 
followed the tracks of this party through the pass to the Nabesna and 
found them to lead down the banks of this stream. We find also t hat 
a prospecting party in charge of Mr. Cooper went through the pass 



1 McNeer was a member of a prospecting party which followed the expedition, and un- engaged 
for this part of the work ..it account of the difficulty of getting any of the regular members of the 
party to undertake it. 



408 CHITINA KIVER AND SKOLAI MOUNTAINS. 

from the Nabesna to the Tanana earlier in the season, on its way from 
Copper Center to the Upper Yukon. 

The season being so far advanced that ice was rapidly forming in 
the streams, and our provisions being reduced to less than ten days' 
rations, we decided to build rafts and make our way down the Nabesna 
and Tanana with all possible haste. Before proceeding down the 
Nabesna very far, however, we met natives, from whom we Learned 
that a portage of five or six days led to the headwaters of the Copper 
River. Securing these natives as guides and packers, we made our 
way overland to Batzulnetas, on Copper River, which was reached 
on the 2d day of October. After rafting down Copper River for 
some miles we found a boat on the bank. Launching this, we made 
our way to the mouth of the Chislechina, where we delayed for three 
days in order to make a side trip for some distance up this stream. 
We then continued down Copper River to Copper Center, which was 
reached on the night of October 10. After a delay of some days at 
Copper Center, we proceeded in a direction almost due south for a dis- 
tance of 20 miles to the Tonsina River, and from here, by way of the 
new military road, we reached Valdes on the 27th of October. 

GENERA! FEATURES. 

TOPOGRAPHY. 

Valdes and tht coast mountains. — The country about Valdes consists 
of a series of rugged, sawtooth ranges, with a general east-and-west 
axis, separated by narrow valleys. A partial submergence of this 
area gave rise to a series of deep, narrow bays or fjords, bordering 
the coast of Prince William Sound. The northernmost of these is 
Port Valdes. The trans-Alaskan military road from Valdes to the 
interior crosses three of these ranges— the first by way of Keystone 
Canyon, a deep, perpendicular-walled gorge, by which Lowe River 
breaks through the range: the second by a pass known as the Lowe 
River divide: and the third by way of the transverse valley occupied 
by the Kanata River. 

Along the coast the valley- are very deep and narrow, and the 
mountains are very jagged and sharp peaked, but northward, par- 
ticularly beyond the Chena, the valleys become more open and the 
mountain outlines become less jagged and more regular and rounded. 
The average elevation is perhaps 6,000 feet. On the coastward side 
are many small glaciers and neve fields, but toward the interior border 
of the range these disappear entirely. 

Ct>j>l»r Rimer Valley. — The southern side of the Tonsina Valley 
marks the northern border of the Coast Range and the beginning of a 
wide. Hat valley, composed of a great thickness of glacial graved and silt 
deposits. This valley extends northward to the Mentasta Mountains 
and westward to the divide separating it from the Cook Inlet drain- 



bohk.] TOPOGRAPHY. 409 

age, while on the eastern side it Le bounded by the Wrangell Mountains. 
Through it Copper River has cut a gorge attaining at times a depth 
of 500 feet and a width of a mile or more. Its tributaries join it 
through corresponding lateral gorges. The gradient due to this cut- 
ting, added to the already high gradient of the valley, makes these 
streams exceedingly swift and torrential. They are further made dan- 
gerous and unfit for boating by the fact that the glacial drift of which 
the valley is composed contains beds of huge bowlders, which are left 
in the river bottoms as the finer material i.s washed away. The bed of 
the Copper River is in places, notably above the mouth of the Tazlina 
River, full of these bowlders. Copper River leaves this valley by fol- 
lowing the border of the coast mountains for some distance south- 
eastward and then breaking through them in a deep, narrow valley, at 
the head of which is Woods Canyon. 

( 'hU i an River Valley. — Just above. Woods Canyon the Copper River 
is joined from the east by the Chitina, a river of about equal volume. 
The valley of the Chitina averages in width from 20 to 40 miles, 
and separates the coast mountains from the Wrangell group. The 
lower part of the Chitina Vail >y is unlike the Copper River basin, 
in that it is not deeply buried under glacial drift, and in that the sur- 
face is composed of a series of low, rounded domes of rock with 
innumerable bogs and lakelets between them. The Chitina follows 
the southern border of this valley, and its tributaries cut across it in 
gulches and canyons. The valley narrows to about 35 miles above 
the mouth of the river. Farther on, where the Chitina is joined by 
the Nizina, its great northern branch, the valley again widens. This 
upper valley is more heavily covered by glacial deposits and is better 
drained, presenting the appearance characteristic of the Copper River 
Valley. The main or central branch of the Chitina rises about due 
east from its confluence with the Nizina in a very high, snow-capped 
range of mountains. Some distance above the mouth of the Nizina 
the < 'liitina is joined by a branch from the south called by the natives 
the Tana. This is said to be extremely swift and full of rapids and 
cataracts, and rises far south toward the coast. Between the Tana 

and the Chitina several large lakes are seen. 

Nizina Ri/oer. For a distance of 6 or 7 miles above its mouth the 
Nizina flows through a rock-walled canyon in a generally southwest- 
erly direction, dust above the canyon it is joined from the north by 
a swift stream draining Kennicott Glacier. From the poinl where it 
leaves the mountains to the head of the canyon, a distance of about 
l.~> miles, it flows through a gravel gorge in a general westerly direc- 
tion. From the glacier in which it heads to the point where it leaves 
the mountains, a distance of from L5 to 20 miles, the stream breaks 
Up into innumerable channels, which migrate back and forth on a 
flood plain sometimes '2 miles wide. This i^ hemmed in by high, often 
perpendicular, rock walls. 



410 CHITINA RIVEK AND SKOLAI MOUNTAINS. 

The Nikolai house, visited by Lieutenant Allen. 1 is just east of the 
great bend where the river leaves the mountain. About 5 miles above 
this the Nizena is joined from the east by a large tributary called the 
Chitistone. This rises in a series- of glaciers flowing down the western 
side of the huge mountain range eastward. 

Hi, coast mountains south of the Chitina River. — The mountains 
south of the Chitina, as seen from the mountains north of its valley, 
present the appearance of a sea of rather uniformly high, closely 
nested peaks, or of a plateau from 5,000 to 6,000 feet high, dissected 
to a depth of from I. (too to 2,000 feet by drainage lines. It is prob- 
able, however, that this appearance is somewhat deceptive, and that 
in reality this area consists of a series of ranges separated by drainage 
lines leading in a general westerly direction toward Copper River. 
This is made more probable by the fact that below the Tana the Chit- 
ina is joined by no important tributary from the south. 

Wrangell Mountains.- North of the Chitina Valley, occupying the 
great bend in Copper River, is a group of four huge, isolated peaks 
joined by high, impassable ranges, the whole a desolate wilderness 
covered by heavy snow and neve fields, the source of innumerable 
glaciers which extend far out into the valleys of the foothills below. 
The central and highest peak, Mount Wrangell, an active volcano, is 
a huge, smooth, rounded dome, with several small cones rising from 
its surface. From one of these vapor rises continually, and periodi- 
cally it sends out greal puffs of steam, black with ashes. About 20 
miles northwest of this is Mount Drum. From its southern side 
Mount Drum appears very jagged, and a large part of it is cut away 
by erosion, presenting, as has been suggested by Schrader, an appear- 
ance of a huge crater with one side blown off. 8 Its northern side, 
however, is affected very much less by erosion, and presents a rounded 
outline exactly like that of Mount Sanford, farther east. Both rise 
majestically above all else around them and present smooth, flowing 
outlines that may he due to the great thickness of snow that .covers 
them. Mount Sanford is nowhere seen cut by erosion as is Mount 
Drum on its southern side. High ridges connect Mount Drum 
and Mount Sanford with Mount Wrangell; the area between them is 
drained by the Sanford River, which flows northeast into the Copper 
River. Mounts Drum and Sanford are supposed to be between L2,000 
and 13,000 feet high. The northern and western slopes of Mount Drum 
merge into the plains of the Copper River Valley, but Mount Sanford 
is surrounded toward the north and east by a wide border of rough, 
jagged foothills.' 

1 Reconnaissance in Alaska, by Lieut. H. T. Allen. 1885. 

-A reconnaissance of a part of Prince William Sound and the Cupper River district, Alaska, by K ('. 
Schrader: Twentieth Ann. Kept. V. S.Geol. Survey, ft. VII. p. :177. 

:l No mountain answering to the location and description of Mount Tillman of the older maps was 
seen by the writer. 



rohn] TOPOGRAPHY. 411 

Southeast from Mount Wrangell and some 25 to 30 miles distant 
from it is Mount Blackburn. This presents a rounded outline only at 
its very top, being cut deeply on all sides by erosion. The divide 
between Mount Drum and Mount Wrangell is an expanse of neve 
fields with isolated, jagged peaks projecting through it. This range 
continues with the same general character in a direction a little north 
of east from Mount Blackburn. Beyond Mount Regal, a peak about 
25 miles from Mount Blackburn, the range is crossed by two breaks 
which are occupied by the Tanana-Nizina glaciers. Beyond these it 
turns southeastward and probably continues with the same general 
characteristics to its junction with the St. Elias Range. 

From the foot of Mount Drum southward, bordering Mount Wran- 
gell and Mount Blackburn, is a series of foothills, very rough and 
jagged in character, averaging from 5,000 to 7,000 feet in elevation, 
attaining around Mount Blackburn a maximum width of about 25 
miles. These continue eastward as the northern border of the Chitina 
Valley. 

The foothills east of Mount Sanford join those of Mount Wrangell 
and form a range with an average elevation of about 7,000 feet, 
which, in continuing in a northeasterly direction, joins the Mentasta 
Mountains and forms a divide between the Copper River Valle} r and 
that of the Nabesna. The Nabesna River is a great western branch of 
the Tanana, draining the entire area east of the Wrangell Mountains, 
which was formerly supposed to belong to the Copper River drainage. 
This river flows in a northeasterly direction and breaks directly 
through the Mentasta Range. 

The very high Skolai Range, alread}' described, terminates abruptly 
on its northern side in a depression about 20 miles wide, forming in 
its central portion the valley of the Upper Tanana River. Westward 
it contracts to a narrow pass and beyond this it forms the valley of 
the Upper Nabesna. To the north of this depression is a range of 
mountains from 7,000 to 8,000 feet high, with very jagged, irregular 
outlines the Xutzotin Range 1 — which is in reality a direct southern 
continuation of the Mentasta Range. The Mentasta Range, which 
extends in a general southeast-northwest direction, forms, as is well 
known, the divide between the Tanana and Copper rivers. Toward 
the northwest this range increases in ruggedness and elevation, culmi- 
nating in Mount Kimball and forming a part of the Great Alaskan 
Range. The south side of this is drained by the Chislechina, one of 
the largest western branches of the Copper River. Along the Upper 
Chislechina and along the southern border of the Mentasta Range is 
a series of low, rounded foothills, and to the west nothing could be seen 
but a continuation of the flat plains of the Copper River Valley. 

1 \ reconnaissance in the Tanana and White river basins, Alaska, in 1898: Twentieth Ann. Rept. 
i S Geol. Survey, Part VII, p. 146. 



412 CHITINA KIVER AND SKOLAI MOUNTAINS. 

CLIMATE AND SEASONS. 

Climatic conditions divide the Copper River district into two distinct 
provinces. Prince William Sound and the seaward side of the coast 
mountains have, owing to the influence of the Japan current, the mod- 
erate temperature and great humidity characteristic of the coast of 
southeastern Alaska. The winters are mild and the summers are cool. 
The temperature seldom falls much below zero, and varies within 
narrow limits, while the precipitation is very abundant and cloudy 
weather the rule rather than the exception. Beyond the coast moun- 
tains the climate resembles that of the Middle Yukon basin, which is 
characterized by extreme cold in winter and moderate heat in summer, 
and by dry, bright, and clear weather. The coast mountains along 
the ( Jopper River Valley are not nearly so high as the St. Elias Moun- 
tains, farther east, and do not so effectually precipitate the moisture 
from the warm ocean winds. The moisture which thus reaches the 
interior gives rise to heavy precipitation, which produces great snow 
fields and glaciers in the Wrangell and Skolai mountains. The south 
sides of these present the heaviest glaciatioa found anywhere in the 
interior of Alaska. On the southern border of these mountains a rainy 
season was encountered during August and early September very much 
like that which prevails at this time annually on the Bering Sea plains 
and along the Lower Yukon and Kuskokwim Rivers. The manner in 
which the clouds constantly hung on the flanks of the Wrangell Moun- 
tains at this season, while the Chitina Valley was bright and clear, was 
very noticeable. The difference in snowfall between the southern and 
the northern side of the Wrangell Mountains was marked; but not to 
be compared with that on the opposite sides of the coast ranges. 

Not the climate alone, but the seasons as well, are different on oppo- 
site sides of the coast mountains. In the coastal region the heavy 
snow does not finally disappear until late in the very short spring, 
which intervenes between the long winter and the very short summer, 
and when it does disappear vegetation springs up with marvelous 
rapidity. In the interior the very much lighter snowfall disappears 
much more rapidly, and the summer season opens from two to three 
weeks earlier than on the coast. Extremely local conditions, due not 
only to difference in elevation but to the angle of incidence of the sun's 
rays, have a marked effect upon the season. This is impressive at 
Valdes. In the early summer, while the snow is disappearing from 
the flood plains and bottom lands of the valley and the conditions here 
are those of March in New England, the southward-facing mountain 
side to the north of the valley will be clothed in green to a considerable 
elevation, with flowers in blossom and vegetation in full foliage, while 
the northward-facing mountain side to the south of the valley is in the 
depth of winter and covered with a thick mantle of snow extending 
almost to tide water. 



Rons.] CLIMATE AND SEASONS. 413 

As the length and progress of the season is of much interest to pros- 
pectors and explorers contemplating work in the interior, a few of the 
leading features of the season of 1899 are appended to serve as a guide. 

When the Copper River Exploring Expedition landed on the 22d 
day of April, the tide-water plains about Valdes were covered with from 
4 to 6 feet of snow, and between the 22d and 24th of April there was 
an additional snowfall of about 18 inches. It was thawing daily, how- 
ever, and by the 15th of May the snow was rapidly disappearing from 
tin; gravel flats. By the 1st of June it was receding up the mountain 
sides and by the loth of June the mountains were hare to the 4,000 or 
5,000 foot level. The glacial streams draining Valdes Glacier and those 
tributary to Lowe River began to rise about June 10. Lowe River 
rose slowly from May 15 to June 15, then subsided somewhat to about 
July It): then it again arose and was at its height about August 15. 
After this it began slowly subsiding. 

We reached the Chitina River on the 15th of July, and at this time 
it was flooding from bank to bank and still rising. The highest water 
seen during the season was on July 28. When we reached the Nizina 
on August 20, the flooding season was past and the water had receded 
considerably. Up to August 1 the weather had been clear and bright, 
but at this time cloudy weather had set in with occasional showers, 
which became more and more marked and still continued when we left 
the Chitina Valley over the glacier to the north. The time when the 
snow line reached its maximum elevation was not accurately determined, 
but it was probabl}- about August 10. On September 1, when we were 
crossing the glacier, the lower limit of snow on it was about 7,500 feet 
and was moving down rapidly from day to da}'. North of the glacier 
the snow line stood at 7,000 feet on September 10. The Tanana Glacier 
was at this time freezing up and the river issuing from it was rapidly 
drying. By September 18 the snow line at the head of the Tanana 
stood at about G, 000 feet. The weather was clear and cold, and ice was 
forming in the streams. 

When we reached the Xabesna River on the 23d of September mush 
ice was running heavily in the main stream, and all the smaller chan- 
nels were frozen over. On crossing the divide between the Xabesna 
and the Copper on September 29 the snow line extended below the 
5,000-foot level; and on the divide, at an elevation of about 6,50(> feet, 
the snow was to L0 inches deep. Mush ice appeared in the Copper, 
at (lie mouth <»f the Slana, about September 25, When we reached 
Copper Center on October lOthe ice in the fiver was running so heav- 
ily that a boat could be managed only with the greatest difficulty. On 
the (rip from Copper Center to Valdes, from October 18 to the 27. 
all small streams in the Copper River Valley were found frozen up. 

The Tonsina, which we crossed on the 21st, was frozen, except a nar- 
row channel through the center. On the divide between the Tonsina 



414 CHITINA RIVER AND SKOLAI MOUNTAINS. 

and the Kanata, at an elevation of 4,000 feet, the snow was 1| feet 
deep, and on the Lowe River divide, at an elevation of 2,600 feet, the 
snow was found over 3 feet deep on the 25th. The snow line reached 
tide water about November 1. 

TIMBER AND VEGETATION. 

Full descriptions of the different species of plants and animals found 
in the different parts of Alaska have been prepared by Dr. Dall and 
many other writers. These probably include most of the species found 
in the Copper River region, and no attempt to add to them can here 
be made. A few words regarding the distribution of those of eco- 
nomic importance, may, however, be useful. 

The elevation of timber line varies considerably in different parts 
of the area. On the islands and coast of Prince William Sound it 
is about 2,000 feet. In the neighborhood of Valdes it is considerably 
less, while in the Chitina and Copper River basins it is between 3,000 
and 3,500 feet, and on the Tanana and Upper Copper it is nearly 
4,500 feet. The interior basins are well timbered except where 
burned over by the natives. This has been done on a very extensive 
scale, and a large amount of timber is annually destroyed by them. 
In places very fine timber is found. As a ride, however, especially at 
the higher altitudes, it is rather short and somewhat scrubby. The 
only timber of importance is spruce. Several kinds of poplar are 
found and the trees sometimes attain considerable size. They grow 
chiefl}' on old gravel bars and river bottoms. At higher elevations 
birch is occasionally found, but it is usually small and of little value. 
Willow and alder, usually as brush, though sometimes attaining a size 
that entitles them to be classed with trees, predominate along the 
upper margin of the timber belt. 

Wherever the timber and the moss which usually covers the ground 
has been destroyed grass flourishes abundantly. Of this there are 
many different kinds, most of which are valuable for both hay and 
grazing, and are consequently of much economic importance in making 
possible the advantageous use of pack animals for transportation 
purposes. 

Blueberries, black and red curfants, cranberries, moss berries, and 
red salmon berries are found in great abundance. The red currant 
here found rivals in size and flavor the domestic currants of the 
States. 

Among the many kinds and varieties of the most beautiful wild 
flowers which flourish everywhere in great abundance, probably the 
most conspicuous is the forget-me-not, which is found far above the 
timber line on the most barren mountains, often at the very edge of 
perpetual ice and snow. 



415 



ANIMAL LIFE. 



According to the testimony of the natives and judging by the great 
number of antlers found, and the remains of traps or fences used by 
the natives for catching them, moose and caribou must have been very 
abundant in the country adjacent to the Wrangell Mountains. Now, 
however, they have either migrated elsewhere or become almost extinct, 
as only a very few are occasionally taken, on the northwestern border of 
the Copper River Valley. Bears are very numerous, but usually of the 
smaller In-own and the black species. No indications were seen of the 
huge hiown bears found on the Aleutian Peninsula. The animals now 
chiefly depended upon by the natives for food are mountain sheep and 
mountain gouts. The sheep of the Wrangell Mountains differ con- 
siderably from those of the Rocky Mountains and differ somewhat 
also from the species found in the vicinity of Cook Inlet and the Upper 
Kuskokwim River. Hundreds of these animals were seen in flocks, at 
times, of as many as a dozen to twenty individuals. They are found, 
however, only at great heights, on craggy and inaccessible mountains 
and are usually most difficult to reach. Martens are trapped in con- 
siderable numbers, particularly by the Tanana natives, and beaver, 
though taken, seem not to be very numerous. Ground squirrels, which 
are so abundant in the western part of Alaska, do not seem to be very 
abundant here. Wolves and foxes, the latter including the black and 
silver-gray varieties, are taken b} r the natives. 

Eagles and ravens are very common and are to be reckoned with 
in leaving fresh meat exposed anywhere away from camp. Brant, 
many different species of ducks, grouse, and ptarmigan are abundant 
and furnish the natives with important items of food. 

Many different varieties of fish are found in the brooks and lakes. 
The salmon, however, is the one of most importance. These run 
up Copper River and its tributaries annually and furnish the natives 
with their only staple article of food. Every native has a ••stick," 
or summer house, and salmon cache at some point along the river, 
where he lives during the summer season, catching and drying 
salmon, and to which he returns after the fall hunt, when the snow 
becomes too deep to travel. Salmon do not reach the Upper Tanana 
River, and the Tanana natives go to the Copper River to catch their 
year's supply. Halibut and cod are abundant in Prince William 
Sound and along the coast. 



Tonsina "/<>/ Lowt r Copper River.— A good trail leads fromTonsina 
Lake eastward along the northern bank of the Tonsina River to a 
point on Copper River about S miles above the mouth of the Tonsina. 
This trail has been carefully marked and cut out and can easily be 



416 CHITINA RIVER AND SKOLAI MOUNTAINS. 

found. From a point where it reaches the upper edge of the Copper 
River gorge it connects with an old Indian trail leading along the 
Copper River bluffs to a point on the Copper about a mile above the 
mouth of the Tonsina. Here a number of bars divide the river into 
several narrow channels, making crossing easy for pack animals. 
Care must, however, be exercised to keep the animals well up toward 
the head of the liars, as the lower ends are often soft and composed of 
quicksand. 

A trail leads from Copper Center down the western side of Copper 
River. This is. however, very irregular and most difficult to travel. 
From a point on the Copper River opposite the mouth of the Tonsina 
an Indian trail leads along the eastern bank of the Copper River for 
the greater part of the distance to the mouth of the Chitina. In 
places, particularly near Indian houses, this is very good, and in others 
it is almost impassable. With comparatively little work a trail could 
be made which, leading hack from Copper River about opposite from 
the Tonsina. and keeping well back from the river valley to avoid the 
lateral draws, would lead in a general southeasterly direction into the 
Chitina Valley. 

To the Kotsina River. -On the eastern side of Copper River about 
5 or (3 miles below the mouth of the Tonsina is the winter house of a 
native known as Belluni. From here a trail leaves Copper River and 
leading almost due east reaches the Kotsina River at the point where 
it emerges from the mountains, a distance of about 10 to V2 miles. 
From here it leads up file northern side of the Kotsina River Valley 
for 8 or 10 miles more. This trail is entirely feasible for pack horses, 
and by means of these the headwaters of the Kotsina can be reached 
at any time except that of the highest Hoods. 

Along the Chitina River. -The general route up the Chitina River 
is the Nikolai trail, leading from Taral over the mountains on the south- 
eidy side of the river to the Nikolai house on the Xizina. This is the 
trail followed by Lieutenant Allen in 1885. It is not feasible for pack 
train. An old Indian trail was found on the northerly side of the river 
leaving the bank about 8 miles above its mouth and running from here 
to the point where the Kuskulana River emerges from the mountains, 
and then following the Kuskulana it crosses the same near the foot of 
the glacier and leads in an easterly direction to the bend in the Lachina. 
This route is well marked out and can be traveled by pack train at 
almost any time of the year. From the Lachina eastward to the Xizina 
a trail was cut during the summer of 1899 which leads through several 
mountain passes and is rather difficult to follow. This may be the best 
route for reaching the Nizina during the time of high water, but at 
any other time a much better trail could easily be made which would 
lead down the Lachina to the toot of the mountains and along these to 
the foot of the Nizina, crossing the Kennicott River at the foot of Ken- 
nicott Glacier. 



bohn.] TRAILS. 417 

It is reported that the Indians formerly reache . t Wo coast at a point 
between Yakutat and Kyak by traveling up the southern branch of 
the Chitina, known by the natives as the Tana. This route involves 
crossing a glacier, and is not now used by the natives. 

Skolai Pans. — : A trail leading from the White River to the Chitina. 
by way of Skolai Pass, used by the natives and followed by Lieuten- 
ant Sehwatka and Dr. Hayes, leaves the Nizena Valley at a point 
several miles above the foot of the glacier, where a valley free from 
glaciers joins it from the east. From the head of this valley a low 
gap leads to the headwaters of the White River over the foot of a 
glacier which Dr. Hayes has named Russell Glacier. 1 In winter the 
natives travel on Skolai Creek, hut in the summer time, when the 
Nizina is flooding-, they use a trail through the mountains leading 
to the Chitistone, and by way of this they reach the Nikolai house. 
This is probably the only route feasible for crossing from the Chitina 
to the White or Tanana. It is said to lie not very difficult for trav- 
eling with a light pack, but it is quite impassable for the use of a 
pack train, or for railroad, or for transporting goods by any other 
means. 

[~]>/>>r Copper River Valley. — From Copper Center northward two 
general trails lead toward Mentasta Pass, one along the western bank 
of the Copper River, and the other in a more or less direct course 
from Copper Center to the mouth of the Slana along the foot of 
Mount Drum, the latter known as the Millard trail. The former 
probably affords the firmer footing, while the latter avoids crossing 
the western tributaries of the Copper. The trail leading from the 
mouth of the Slana to Mentasta Pass is well marked and easily followed. 
From the mouth of the Chestochena a good trail leads up the river 
along its western bank for a distance of 60 to 75 miles. From the 
mouth of the Slana the trail leads along the eastern bank of the Cop- 
per for a distance of about 10 miles to Batzulnetas. 

From the <'<>]>/></■ tothe Nabesna <(n<l Tanana. — From Batzulnetas a 
good trail leads in a general southerly direction for a distance of about 
L0 miles, where it forks, leading by three different passes to the 
Nabesna River. These arc all feasible for horse trails, and each is 
advantageous according to the point on the Nabesna that is to be 
reached. The western one. by way of Lake Tanada, was used by 
prospecting parties traveling with pack train during the season of L899, 
and the central one was used as a sled route. The eastern one, how- 
ever, is the most practicable and the easiest, particularly for reaching 
the trail from the Nabesna to the Tanana and White rivers. The west- 
ern one, which was traveled by pack (rains, is well marked up. but 
the others are difficult to follow and require guides. 



n expedition through the Yukon district, l>y c. w. Hayes: Nat.Qeog. Mag.,Maj 15,1892. 
21 OEOL, PT 2 27 



418 CHITINA RIVER AND SKOLAI MOUNTAINS. 

The trail from the Nabesna to the Tanana leads to one of two 
passes. The northern one, the most direct and the one used by the 
natives, is not feasible for pack horses, while the one a little farther 
south is. This is the only part of the route that offers any difficulty 
whatever for railroading, but the difficulties are not such that they 
can not be readily overcome. 

PACK TRAINS. 

The military road and the network of trails found in the Copper 
River Valley make pack trains the only convenient and satisfactory 
means of transporting goods; they can lie used to advantage from 
about the loth of dune to about the loth of October, and they have been 
adopted almost exclusively by the prospectors now working in the 
country. If large quantities of goods are to be transported, this can 
in some cases be done to advantage by sledding with horses on the ice 
of the rivers during the months of February, March, and April. 

The experience of the pas! year's work with different outfits prompts 
the following suggestions: A stocky Montana ranch horse weighing 
about L,200 pounds, which had not been yi>vd as a harness horse and 
which had not been stable fed. was found to be the most satisfactory. 
Such horses were bough! for about $40 and cost about an equal amount 
for transportation. A well-fitting double-cinch sawbuck saddle, with- 
out breeching or breastpad, with twoheai y blankets under it. was found 
the most satisfactory. Saddlebags or panniers made of canvas well 
trimmed with leather are a great convenience and economy. These 
should lie made just long and wide enough to accommodate a 50-pound 
sack of Hour and should lie in depth a little less than twice their width. 
They should be fitted with straps by which to bang them to the saddle 
horn. All goods should be packed in sacks and all forms of boxes 
carefully avoided. A very useful precaution is to have a couple of 
cans of baking powder well buried in each sack of Hour. Pack covers 
made of strong canvas about 7 feet square are very useful, and a far- 
rier's kit. with a sufficient supplj of horseshoes finished and ready for 
the horses* feet, must under no circumstances lie omitted. Two men 
can handle twelve horses without much difficulty, but to do so to 
advantage they should be allowed one saddle horse. Such horses as 
above mentioned will readily carry 200 pounds each. 

GEOIiOGl 

PRELIMINARY STATEMENT. 

In exploration, where ignorance of the difficulties and obstacles to be 
met and overcome makes it accessary to proceed as rapidly as possible 
and to avoid every form of dehu . geological observations must neces- 
sarily be brief and fragmentary. This was particularly true of the trip 



Rohn-.] VALDES TO THE TONSINA. . 419 

on which this report is based. It was undertaken for the War Depart- 
ment with the primary object of doing topographic work. In addi- 
tion to topographic work it was necessary to pilot a pack train through 
a difficult and unknown country, and later to continue by back-packing 
under great pressure. Therefore the geologic notes necessarily con- 
sist of general observations obtained incidentally and the specimens 
consist of such as could conveniently be picked up along the route. 
In a practically unknown area even such information as that gathered 
is useful as a guide to prospectors and to further work in the area. 
This being the case, the following report is warranted even if the work 
upon which it is based was very fragmentary. 

VALDES TO THE TONSINA RIVER. 

The rocks of the area about Valdes and along Lowe River have been 
examined and described by Schrader. 1 These consist of a series of 
interbedded quartzites, arkoses, slates, and shales, and occasionally 
some mica-schist. The rocks are very much faulted and folded. The 
strike is generally about east and west and the dip steeply north. The 
dip is rather uniform, and if the valleys between the ranges present a 
continuation of the series as